\input texinfo @c %**start of header @setfilename sh-utils.info @settitle GNU shell utilities @c %**end of header @include version.texi @c Define new indices for file names and options. @defcodeindex fl @defcodeindex op @c Put everything in one index (arbitrarily chosen to be the concept index). @syncodeindex fl cp @syncodeindex fn cp @syncodeindex ky cp @syncodeindex op cp @syncodeindex pg cp @syncodeindex vr cp @ifinfo @set Francois Franc,ois @end ifinfo @tex @set Francois Fran\noexpand\ptexc cois @end tex @ifinfo @format START-INFO-DIR-ENTRY * Shell utilities: (sh-utils). GNU shell utilities. * basename: (sh-utils)basename invocation. Strip directory and suffix. * date: (sh-utils)date invocation. Print/set system date and time. * dirname: (sh-utils)dirname invocation. Strip non-directory suffix. * echo: (sh-utils)echo invocation. Print a line of text. * env: (sh-utils)env invocation. Modify the environment. * expr: (sh-utils)expr invocation. Evaluate expressions. * false: (sh-utils)false invocation. Do nothing, unsuccessfully. * groups: (sh-utils)groups invocation. Print group names a user is in. * hostname: (sh-utils)hostname invocation. Print or set system name. * id: (sh-utils)id invocation. Print real/effective uid/gid. * logname: (sh-utils)logname invocation. Print current login name. * nice: (sh-utils)nice invocation. Modify scheduling priority. * nohup: (sh-utils)nohup invocation. Immunize to hangups. * pathchk: (sh-utils)pathchk invocation. Check file name portability. * printenv: (sh-utils)printenv invocation. Print environment variables. * printf: (sh-utils)printf invocation. Format and print data. * pwd: (sh-utils)pwd invocation. Print working directory. * sleep: (sh-utils)sleep invocation. Delay for a specified time. * stty: (sh-utils)stty invocation. Print/change terminal settings. * su: (sh-utils)su invocation. Modify user and group id. * tee: (sh-utils)tee invocation. Redirect to multiple files. * test: (sh-utils)test invocation. File/string tests. * true: (sh-utils)true invocation. Do nothing, successfully. * tty: (sh-utils)tty invocation. Print terminal name. * uname: (sh-utils)uname invocation. Print system information. * users: (sh-utils)users invocation. Print current user names. * who: (sh-utils)who invocation. Print who is logged in. * whoami: (sh-utils)whoami invocation. Print effective user id. * yes: (sh-utils)yes invocation. Print a string indefinitely. END-INFO-DIR-ENTRY @end format @end ifinfo @ifinfo This file documents the GNU shell utilities. Copyright (C) 1994 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. @end ifinfo @titlepage @title GNU @code{sh-utils} @subtitle A set of shell utilities @subtitle for version @value{VERSION}, @value{RELEASEDATE} @author David MacKenzie et al. @page @vskip 0pt plus 1filll Copyright @copyright{} 1994 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. @end titlepage @ifinfo @node Top @top GNU shell utilities @cindex shell utilities @cindex utilities for shell programming This manual minimally documents version @value{VERSION} of the GNU shell utilities. @menu * Introduction:: Caveats, overview, and authors. * Common options:: Common options. * Date input formats:: Specifying date strings. * Printing text:: echo printf yes * Conditions:: false true test expr * Redirection:: tee * File name manipulation:: dirname basename pathchk * Working context:: pwd stty printenv tty * User information:: id logname whoami groups users who * System context:: date uname hostname * Modified command invocation:: env nice nohup su * Delaying:: sleep * Index:: General index. @end menu @end ifinfo @node Introduction @chapter Introduction @cindex introduction First of all, this manual is incomplete. The @code{stty} section, in particular, needs substantial reorganization and additional explanatory text before it will be up to the standard of other GNU manuals. Explanatory text in general is lacking; the manual presently assumes you pretty much know what to do, and just need to be reminded of how. Thus, if you are interested, please get involved in improving this manual. The entire GNU community will benefit. Some of these programs are useful only when writing shell scripts; utilities like these are, in fact, the ``language'' of shell scripts (to a great extent). Others are occasionally useful interactively. @cindex POSIX.2 The GNU shell utilities are mostly compatible with the POSIX.2 standard. @c This paragraph appears in all of fileutils.texi, textutils.texi, and @c sh-utils.texi too -- so be sure to keep them consistent. @cindex bugs, reporting Please report bugs to @samp{bug-gnu-utils@@prep.ai.mit.edu}. Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug: your input, what you expected, what you got, and why it is wrong. Diffs are welcome, but please include a description of the problem as well, since this is sometimes difficult to infer. @xref{Bugs, , , gcc, GNU CC}. @cindex history @cindex MacKenzie, David @cindex Meyering, Jim @c Sorry, but the @value trick doesn't work with TeX in indexing @c commands, and I don't want to fix it right now. --karl. @cindex Pinard, Francois @cindex Berry, Karl @cindex Stallman, Richard This manual is based on the Unix man pages in the distribution, which were originally written by David MacKenzie and updated by Jim Meyering. @value{Francois} Pinard did the initial conversion to Texinfo format. Karl Berry did the indexing, some reorganization, and editing of the results. Richard Stallman contributed his usual invaluable insights to the overall process. @node Common options @chapter Common options @cindex common options Certain options are available in all these programs. Rather than writing identical descriptions for each of the programs, they are described here. (In fact, every GNU program accepts (or should accept) these options.) Many of these programs take arbitrary strings as arguments. In those cases, @samp{--help} and @samp{--version} are taken as these options only if there is one and exactly one command line argument. @table @samp @item --help @opindex --help @cindex help, online Print a usage message listing all available options, then exit successfully. @item --version @opindex --version @cindex version number, finding Print the version number, then exit successfully. @end table @include getdate.texi @node Printing text @chapter Printing text @cindex printing text, commands for @cindex commands for printing text This section describes commands that display text strings. @menu * echo invocation:: Print a line of text. * printf invocation:: Format and print data. * yes invocation:: Print a string until interrupted. @end menu @node echo invocation @section @code{echo}: Print a line of text @pindex echo @cindex displaying text @cindex printing text @cindex text, displaying @cindex arbitrary text, displaying Synopsis: @example echo [@var{option}]@dots{} [@var{string}]@dots{} @end example @code{echo} writes each given @var{string} to standard output, with a space between each and a newline after the last one. The program accepts the following options. Also see @ref{Common options}. @table @samp @item -n @opindex -n Do not output the trailing newline. @item -e @opindex -e @cindex backslash escapes Enable interpretation of the following backslash-escaped characters in each @var{string}: @table @samp @item \a alert (bell) @item \b backspace @item \c suppress trailing newline @item \f form feed @item \n new line @item \r carriage return @item \t horizontal tab @item \v vertical tab @item \\ backslash @item \@var{nnn} the character whose ASCII code is @var{nnn} (octal); if @var{nnn} is not a valid octal number, it is printed literally. @end table @end table @node printf invocation @section @code{printf}: Format and print data @pindex printf Synopsis: @example printf @var{format} [@var{argument}]@dots{} @end example @code{printf} prints the @var{format} string, interpreting @samp{%} directives and @samp{\} escapes in the same way as the C @code{printf} function. The @var{format} argument is re-used as necessary to convert all of the given @var{argument}s. @code{printf} has one additional directive, @samp{%b}, which prints its argument string with @samp{\} escapes interpreted in the same way as in the @var{format} string. @kindex \0ooo @kindex \0xhhh @code{printf} interprets @samp{\0ooo} in @var{format} as an octal number (if @var{ooo} is 0 to 3 octal digits) specifying a character to print, and @samp{\xhhh} as a hexadecimal number (if @var{hhh} is 1 to 3 hex digits) specifying a character to print. @kindex \c An additional escape, @samp{\c}, causes @code{printf} to produce no further output. The only options are a lone @samp{--help} or @samp{--version}. @xref{Common options}. @node yes invocation @section @code{yes}: Print a string until interrupted @pindex yes @cindex repeated output of a string @code{yes} prints the command line arguments, separated by spaces and followed by a newline, forever until it is killed. If no arguments are given, it prints @samp{y} followed by a newline forever until killed. The only options are a lone @samp{--help} or @samp{--version}. @xref{Common options}. @node Conditions @chapter Conditions @cindex conditions @cindex commands for exit status @cindex exit status commands This section describes commands that are primarily useful for their exit status, rather than their output. Thus, they are often used as the condition of shell @code{if} statements, or as the last command in a pipeline. @menu * false invocation:: Do nothing, unsuccessfully. * true invocation:: Do nothing, successfully. * test invocation:: Check file types and compare values. * expr invocation:: Evaluate expressions. @end menu @node false invocation @section @code{false}: Do nothing, unsuccessfully @pindex false @cindex exit status of @code{true} @cindex failure exit status @code{false} does nothing except return an exit status of 1, meaning @dfn{failure}. It can be used as a place holder in shell scripts where an unsuccessful command is needed. Any arguments are ignored, except for a lone @samp{--help} or @samp{--version} (@pxref{Common options}). @node true invocation @section @code{true}: Do nothing, successfully @pindex true @cindex do nothing, successfully @cindex no-op @cindex successful exit @cindex exit status of @code{true} @code{true} does nothing except return an exit status of 0, meaning @dfn{success}. It can be used as a place holder in shell scripts where a successful command is needed, although the shell built-in command @code{:} (colon) may be faster. Any arguments are ignored, except for a lone @samp{--help} or @samp{--version} (@pxref{Common options}). @node test invocation @section @code{test}: Check file types and compare values @pindex test @cindex check file types @cindex compare values @cindex expression evaluation @code{test} returns a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression @var{expr}. Each part of the expression must be a separate argument. @code{test} has file status checks, string operators, and numeric comparison operators. @cindex conflicts with shell built-ins @cindex built-in shell commands, conflicts with Because most shells have a built-in command by the same name, using the unadorned command name in a script or interactively may get you different functionality than that described here. Besides the options below, @code{test} accepts a lone @samp{--help} or @samp{--version}. @xref{Common options}. A single non-option argument is also allowed: @code{test} returns true if the argument is not null. @menu * File type tests:: -[bcdfhLpSt] * Access permission tests:: -[gkruwxOG] * File characteristics tests:: -e -s -nt -ot -ef * String tests:: -z -n = != * Numeric tests:: -eq -ne -lt -le -gt -ge * Connectives for test:: ! -a -o @end menu @node File type tests @subsection File type tests @cindex file type tests These options test for particular types of files. (Everything's a file, but not all files are the same!) @table @samp @item -b @var{file} @opindex -b @cindex block special check True if @var{file} exists and is a block special device. @item -c @var{file} @opindex -c @cindex character special check True if @var{file} exists and is a character special device. @item -d @var{file} @opindex -d @cindex directory check True if @var{file} exists and is a directory. @item -f @var{file} @opindex -f @cindex regular file check True if @var{file} exists and is a regular file. @item -h @var{file} @itemx -L @var{file} @opindex -L @opindex -h @cindex symbolic link check True if @var{file} exists and is a symbolic link. @item -p @var{file} @opindex -p @cindex named pipe check True if @var{file} exists and is a named pipe. @item -S @var{file} @opindex -S @cindex socket check True if @var{file} exists and is a socket. @item -t [@var{fd}] @opindex -t @cindex terminal check True if @var{fd} is opened on a terminal. If @var{fd} is omitted, it defaults to 1 (standard output). @end table @node Access permission tests @subsection Access permission tests @cindex access permission tests @cindex permission tests These options test for particular access permissions. @table @samp @item -g @var{file} @opindex -g @cindex set-group-id check True if @var{file} exists and has its set-group-id bit set. @item -k @var{file} @opindex -k @cindex sticky bit check True if @var{file} has its @dfn{sticky} bit set. @item -r @var{file} @opindex -r @cindex readable file check True if @var{file} exists and is readable. @item -u @var{file} @opindex -u @cindex set-user-id check True if @var{file} exists and has its set-user-id bit set. @item -w @var{file} @opindex -w @cindex writable file check True if @var{file} exists and is writable. @item -x @var{file} @opindex -x @cindex executable file check True if @var{file} exists and is executable. @item -O @var{file} @opindex -O @cindex owned by effective uid check True if @var{file} exists and is owned by the current effective user id. @item -G @var{file} @opindex -G @cindex owned by effective gid check True if @var{file} exists and is owned by the current effective group id. @end table @node File characteristics tests @subsection File characteristics tests @cindex file characteristics tests These options test other file characteristics. @table @samp @item -e @var{file} @opindex -e @cindex existence-of-file check True if @var{file} exists. @item -s @var{file} @opindex -s @cindex nonempty file check True if @var{file} exists and has a size greater than zero. @item @var{file1} -nt @var{file2} @opindex -nt @cindex newer-than file check True if @var{file1} is newer (according to modification date) than @var{file2}. @item @var{file1} -ot @var{file2} @opindex -ot @cindex older-than file check True if @var{file1} is older (according to modification date) than @var{file2}. @item @var{file1} -ef @var{file2} @opindex -ef @cindex same file check @cindex hard link check True if @var{file1} and @var{file2} have the same device and inode numbers, i.e., if they are hard links to each other. @end table @node String tests @subsection String tests @cindex string tests These options test string characteristics. Strings are not quoted for @code{test}, though you may need to quote them to protect characters with special meaning to the shell, e.g., spaces. @table @samp @item -z @var{string} @opindex -z @cindex zero-length string check True if the length of @var{string} is zero. @item -n @var{string} @itemx @var{string} @opindex -n @cindex nonzero-length string check True if the length of @var{string} is non-zero. @item @var{string1} = @var{string2} @opindex = @cindex equal string check True if the strings are equal. @item @var{string1} != @var{string2} @opindex != @cindex not-equal string check True if the strings are not equal. @end table @node Numeric tests @subsection Numeric tests @cindex numeric tests @cindex arithmetic tests Numeric relationals. The arguments must be entirely numeric (possibly negative), or the special expression @w{@code{-l @var{string}}}, which evaluates to the length of @var{string}. @table @samp @item @var{arg1} -eq @var{arg2} @itemx @var{arg1} -ne @var{arg2} @itemx @var{arg1} -lt @var{arg2} @itemx @var{arg1} -le @var{arg2} @itemx @var{arg1} -gt @var{arg2} @itemx @var{arg1} -ge @var{arg2} @opindex -eq @opindex -ne @opindex -lt @opindex -le @opindex -gt @opindex -ge These arithmetic binary operators return true if @var{arg1} is equal, not-equal, less-than, less-than-or-equal, greater-than, or greater-than-or-equal than @var{arg2}, respectively. @end table For example: @example test -1 -gt -2 && echo yes @result{} yes test -l abc -gt 1 && echo yes @result{} yes test 0x100 -eq 1 @error{} test: integer expression expected before -eq @end example @node Connectives for test @subsection Connectives for @code{test} @cindex logical connectives @cindex connectives, logical The usual logical connectives. @table @samp @item ! @var{expr} @opindex ! True if @var{expr} is false. @item @var{expr1} -a @var{expr2} @opindex -a @cindex logical and operator @cindex and operator True if both @var{expr1} and @var{expr2} are true. @item @var{expr1} -o @var{expr2} @opindex -o @cindex logical or operator @cindex or operator True if either @var{expr1} or @var{expr2} is true. @end table @node expr invocation @section @code{expr}: Evaluate expressions @pindex expr @cindex expression evaluation @cindex evaluation of expressions @code{expr} evaluates an expression and writes the result on standard output. Each token of the expression must be a separate argument. Operands are either numbers or strings. @code{expr} coerces anything appearing in an operand position to an integer or a string depending on the operation being applied to it. Strings are not quoted for @code{expr}, though you may need to quote them to protect characters with special meaning to the shell, e.g., spaces. @cindex parentheses for grouping Operators may given as infix symbols or prefix keywords. Parentheses may be used for grouping in the usual manner (you must quote parentheses to avoid the shell evaluating them, however). @cindex exit status of @code{expr} Exit status: @display 0 if the expression is neither null nor 0, 1 if the expression is null or 0, 2 for invalid expressions. @end display @menu * Relations for expr:: | & < <= = == != >= > * Numeric expressions:: + - * / % * String expressions:: : match substr index length * Examples of expr:: Examples. @end menu @node Relations for expr @subsection Relations for @code{expr} @cindex connectives, logical @cindex logical connectives @cindex relations, numeric or string The usual logical connectives and relations, in order of precedence. @table @samp @item | @kindex | @cindex logical or operator @cindex or operator Yields its first argument if it is neither null nor 0, otherwise its second argument. @item & @kindex & @cindex logical and operator @cindex and operator Yields its first argument if neither argument is null or 0, otherwise 0. @item < <= = == != >= > @kindex < @kindex <= @kindex = @kindex == @kindex > @kindex >= @cindex comparison operators Compare the arguments and return 1 if the relation is true, 0 otherwise. @code{==} is a synonym for @code{=}. @code{expr} first tries to coerce both arguments to numbers and do a numeric comparison; if either coercion fails, it does a lexicographic comparison. @end table @node Numeric expressions @subsection Numeric expressions @cindex numeric expressions @cindex expressions, numeric Numeric operators, in order of increasing precedence. The connectives (previous section) have higher precedence, the string operators (following section) have lower. @table @samp @item + - @kindex + @kindex - @cindex addition @cindex subtraction Addition and subtraction. Both arguments are coerced to numbers; an error occurs if this cannot be done. @item * / % @kindex * @kindex / @kindex % @cindex multiplication @cindex division @cindex remainder Multiplication, division, remainder. Both arguments are coerced to numbers; an error occurs if this cannot be done. @end table @node String expressions @subsection String expressions @cindex string expressions @cindex expressions, string String operators. These have lowest precedence. @table @samp @item @var{string} : @var{regex} @cindex pattern matching @cindex regular expression matching @cindex matching patterns Perform pattern matching. The arguments are coerced to strings and the second is considered to be a (basic, a la @code{grep}) regular expression, with a @code{^} implicitly prepended. The first argument is then matched against this regular expression. If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the @code{:} expression returns the part of @var{string} that matched the subexpression; otherwise, it returns the number of characters matched. If the match fails, the @code{:} operator returns the null string if @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0. Only the first @samp{\( @dots{} \)} pair is relevant to the return value; additional pairs are meaningful only for grouping the regular expression operators. @xref{Top, , Regular Expression Library, regex, Regex}, for details of regular expression syntax. @item match @var{string} @var{regex} @findex match An alternative way to do pattern matching. This is the same as @w{@samp{@var{string} : @var{regex}}}. @item substr @var{string} @var{position} @var{length} @findex substr Returns the substring of @var{string} beginning at @var{position} with length at most @var{length}. If either @var{position} or @var{length} is negative or non-numeric, returns the null string. @item index @var{string} @var{character-class} @findex index Returns the first position in @var{string} where the first character in @var{charset} was found. If no character in @var{charset} is found in @var{string}, return 0. @item length @var{string} @findex length Returns the length of @var{string}. @end table The keywords cannot be used as strings. @node Examples of expr @subsection Examples of @code{expr} @cindex examples of @code{expr} Here are a few examples, including quoting for shell metacharacters. To add 1 to the shell variable @code{foo}, in Bourne-compatible shells: @example foo=`expr $foo + 1` @end example To print the non-directory part of the file name stored in @code{$fname}, which need not contain a @code{/}. @example expr $fname : '.*/\(^.*\)' '^|' $fname @end example @example expr abc : 'a\(.\)c' @result{} b expr index abcdef cz @result{} 3 expr index index a @error{} expr: syntax error @end example @node Redirection @chapter Redirection @cindex redirection @cindex commands for redirection Unix shells commonly provide several forms of @dfn{redirection}---ways to change the input source or output destination of a command. But one useful redirection is performed by a separate command, not by the shell; it's described here. @menu * tee invocation:: Redirect output to multiple files. @end menu @node tee invocation @section @code{tee}: Redirect output to multiple files @pindex tee @cindex pipe fitting @cindex destinations, multiple output @cindex read from stdin and write to stdout and files The @code{tee} command copies standard input to standard output and also to any files given as arguments. This is useful when you want not only to send some data down a pipe, but also to save a copy. Synopsis: @example tee [@var{option}]@dots{} [@var{file}]@dots{} @end example If a file being written to does not already exist, it is created. If a file being written to already exists, the data it previously contained is overwritten unless the @code{-a} option is used. The program accepts the following options. Also see @ref{Common options}. @table @samp @item -a @itemx --append @opindex -a @opindex --append Append standard input to the given files rather than overwriting them. @item -i @itemx --ignore-interrupts @opindex -i @opindex --ignore-interrupts Ignore interrupt signals. @end table @node File name manipulation @chapter File name manipulation @cindex file name manipulation @cindex manipulation of file names @cindex commands for file name manipulation This section describes commands that manipulate file names. @menu * basename invocation:: Strip directory and suffix from a file name. * dirname invocation:: Strip non-directory suffix from a file name. * pathchk invocation:: Check file name portability. @end menu @node basename invocation @section @code{basename}: Strip directory and suffix from a file name @pindex basename @cindex strip directory and suffix from file names @cindex directory, stripping from file names @cindex suffix, stripping from file names @cindex file names, stripping directory and suffix @cindex leading directory components, stripping Synopsis: @example basename @var{name} [@var{suffix}] @end example The @code{basename} command removes any leading directory components from @var{name}. If @var{suffix} is specified and is identical to the end of @var{name}, it is removed from @var{name} as well. @code{basename} prints the result on standard output. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node dirname invocation @section @code{dirname}: Strip non-directory suffix from a file name @pindex dirname @cindex directory components, printing @cindex stripping non-directory suffix @cindex non-directory suffix, stripping Synopsis: @example dirname @var{name} @end example @code{dirname} prints all but the final slash-delimited component of @var{name}. If @var{name} is a single component, @code{dirname} prints @samp{.} (meaning the current directory). The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node pathchk invocation @section @code{pathchk}: Check file name portability @pindex pathchk @cindex file names, checking validity and portability @cindex valid file names, checking for @cindex portable file names, checking for Synopsis: @example pathchk [@var{option}]@dots{} @var{name}@dots{} @end example For each @var{name}, @code{pathchk} prints a message if any of these conditions is true: @enumerate @item one of the existing directories in @var{name} does not have search (execute) permission, @item the length of @var{name} is larger than its filesystem's maximum file name length, @item the length of one component of @var{name}, corresponding to an existing directory name, is larger than its filesystem's maximum length for a file name component. @end enumerate The program accepts the following option. Also see @ref{Common options}. @table @samp @item -p @itemx --portability @opindex -p @opindex --portability Instead of performing length checks on the underlying filesystem, test the length of each file name and its components against the POSIX.1 minimum limits for portability. Also check that the file name contains no characters not in the portable file name character set. @end table @cindex exit status of @code{pathchk} Exit status: @display 0 if all specified file names passed all of the tests, 1 otherwise. @end display @node Working context @chapter Working context @cindex working context @cindex commands for printing the working context This section describes commands that display or alter the context in which you are working: the current directory, the terminal settings, and so forth. See also the user-related commands in the next section. @menu * pwd invocation:: Print working directory. * stty invocation:: Print or change terminal characteristics. * printenv invocation:: Print environment variables. * tty invocation:: Print file name of terminal on standard input. @end menu @node pwd invocation @section @code{pwd}: Print working directory @pindex pwd @cindex print name of current directory @cindex current working directory, printing @cindex working directory, printing @cindex symbolic links and @code{pwd} @code{pwd} prints the fully resolved name of the current directory. That is, all components of the printed name will be actual directory names---none will be symbolic links. @cindex conflicts with shell built-ins @cindex built-in shell commands, conflicts with Because most shells have a built-in command by the same name, using the unadorned command name in a script or interactively may get you different functionality than that described here. The only options are a lone @samp{--help} or @samp{--version}. @xref{Common options}. @node stty invocation @section @code{stty}: Print or change terminal characteristics @pindex stty @cindex change or print terminal settings @cindex terminal settings @cindex line settings of terminal If given no arguments, @code{stty} prints the baud rate, line discipline number (on systems that support it), and line settings that have been changed from the values set by @samp{stty sane}. Mode reading and setting are performed on the tty line connected to standard input. @code{stty} accepts many non-option arguments that change aspects of the terminal line operation, as described below. Synopses: @example stty [@var{setting}]@dots{} stty [@var{option}] @end example The program accepts the following options. Also see @ref{Common options}. @table @samp @item -a @itemx --all @opindex -a @opindex --all Print all current settings in human-readable form. @item -g @itemx --save @opindex -g @opindex --save @cindex machine-readable @code{stty} output Print all current settings in a form that can be used as an argument to another @code{stty} command to restore the current settings. @end table Many settings can be turned off by preceding them with a @samp{-}. Such arguments are marked below with ``May be negated'' in their description. The descriptions themselves refer to the positive case, that is, when @emph{not} negated (unless stated otherwise, of course). Some settings are not available on all POSIX systems, since they use extensions. Such arguments are marked below with ``Non-POSIX'' in their description. On non-POSIX systems, those or other settings also may not be available, but it's not feasible to document all the variations: just try it and see. @menu * Control:: Control settings * Input:: Input settings * Output:: Output settings * Local:: Local settings * Combination:: Combination settings * Characters:: Special characters * Special:: Special settings @end menu @node Control @subsection Control settings @cindex control settings Control settings: @table @samp @item parenb @opindex parenb @cindex two-way parity Generate parity bit in output and expect parity bit in input. May be negated. @item parodd @opindex parodd @cindex odd parity @cindex even parity Set odd parity (even if negated). May be negated. @item cs5 @itemx cs6 @itemx cs7 @itemx cs8 @opindex cs@var{n} @cindex character size @cindex eight-bit characters Set character size to 5, 6, 7, or 8 bits. @item hup @itemx hupcl @opindex hup[cl] Send a hangup signal when the last process closes the tty. May be negated. @item cstopb @opindex cstopb @cindex stop bits Use two stop bits per character (one if negated). May be negated. @item cread @opindex cread Allow input to be received. May be negated. @item clocal @opindex clocal @cindex modem control Disable modem control signals. May be negated. @item crtscts @opindex crtscts @cindex hardware flow control @cindex flow control, hardware @cindex RTS/CTS flow control Enable RTS/CTS flow control. Non-POSIX. May be negated. @end table @node Input @subsection Input settings @cindex input settings @table @samp @item ignbrk @opindex ignbrk @cindex breaks, ignoring Ignore breaks. May be negated. @item brkint @opindex brkint @cindex breaks, cause interrupts Make breaks cause an interrupt signal. May be negated. @item ignpar @opindex ignpar @cindex parity, ignoring Ignore parity errors. May be negated. @item parmrk @opindex parmrk @cindex parity errors, marking Mark parity errors (with a 255-0-character sequence). May be negated. @item inpck @opindex inpck Enable input parity checking. May be negated. @item istrip @opindex istrip @cindex eight-bit input Clear high (8th) bit of input characters. May be negated. @item inlcr @opindex inlcr @cindex newline, translating to return Translate newline to carriage return. May be negated. @item igncr @opindex igncr @cindex return, ignoring Ignore carriage return. May be negated. @item icrnl @opindex icrnl @cindex return, translating to newline Translate carriage return to newline. May be negated. @item ixon @opindex ixon @kindex C-s/C-q flow control @cindex XON/XOFF flow control Enable XON/XOFF flow control (that is, @key{CTRL-s}/@key{CTRL-Q}). May be negated. @item ixoff @itemx tandem @opindex ixoff @opindex tandem @cindex software flow control @cindex flow control, software Enable sending of @code{stop} character when the system input buffer is almost full, and @code{start} character when it becomes almost empty again. May be negated. @item iuclc @opindex iuclc @cindex uppercase, translating to lowercase Translate uppercase characters to lowercase. Non-POSIX. May be negated. @item ixany @opindex ixany Allow any character to restart output (only the start character if negated). Non-POSIX. May be negated. @item imaxbel @opindex imaxbel @cindex beeping at input buffer full Enable beeping and not flushing input buffer if a character arrives when the input buffer is full. Non-POSIX. May be negated. @end table @node Output @subsection Output settings @cindex output settings These arguments specify output-related operations. @table @samp @item opost @opindex opost Postprocess output. May be negated. @item olcuc @opindex olcuc @cindex lowercase, translating to output Translate lowercase characters to uppercase. Non-POSIX. May be negated. @item ocrnl @opindex ocrnl @cindex return, translating to newline Translate carriage return to newline. Non-POSIX. May be negated. @item onlcr @opindex onlcr @cindex newline, translating to crlf Translate newline to carriage return-newline. Non-POSIX. May be negated. @item onocr @opindex onocr Do not print carriage returns in the first column. Non-POSIX. May be negated. @item onlret @opindex onlret Newline performs a carriage return. Non-POSIX. May be negated. @item ofill @opindex ofill @cindex pad instead of timing for delaying Use fill (padding) characters instead of timing for delays. Non-POSIX. May be negated. @item ofdel @opindex ofdel @cindex pad character Use delete characters for fill instead of null characters. Non-POSIX. May be negated. @item nl1 @itemx nl0 @opindex nl@var{n} Newline delay style. Non-POSIX. @item cr3 @itemx cr2 @itemx cr1 @itemx cr0 @opindex cr@var{n} Carriage return delay style. Non-POSIX. @item tab3 @itemx tab2 @itemx tab1 @itemx tab0 @opindex tab@var{n} Horizontal tab delay style. Non-POSIX. @item bs1 @itemx bs0 @opindex bs@var{n} Backspace delay style. Non-POSIX. @item vt1 @itemx vt0 @opindex vt@var{n} Vertical tab delay style. Non-POSIX. @item ff1 @itemx ff0 @opindex ff@var{n} Form feed delay style. Non-POSIX. @end table @node Local @subsection Local settings @cindex local settings @table @samp @item isig @opindex isig Enable @code{interrupt}, @code{quit}, and @code{suspend} special characters. May be negated. @item icanon @opindex icanon Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt} special characters. May be negated. @item iexten @opindex iexten Enable non-POSIX special characters. May be negated. @item echo @opindex echo Echo input characters. May be negated. @item echoe @itemx crterase @opindex echoe @opindex crterase Echo @code{erase} characters as backspace-space-backspace. May be negated. @item echok @opindex echok @cindex newline echoing after @code{kill} Echo a newline after a @code{kill} character. May be negated. @item echonl @opindex echonl @cindex newline, echoing Echo newline even if not echoing other characters. May be negated. @item noflsh @opindex noflsh @cindex flushing, disabling Disable flushing after @code{interrupt} and @code{quit} special characters. May be negated. @item xcase @opindex xcase @cindex case translation Enable input and output of uppercase characters by preceding their lowercase equivalents with @samp{\}, when @code{icanon} is set. Non-POSIX. May be negated. @item tostop @opindex tostop @cindex background jobs, stopping at terminal write Stop background jobs that try to write to the terminal. Non-POSIX. May be negated. @item echoprt @itemx prterase @opindex echoprt @opindex prterase Echo erased characters backward, between @samp{\} and @samp{/}. Non-POSIX. May be negated. @item echoctl @itemx ctlecho @opindex echoctl @opindex ctlecho @cindex control characters, using @samp{^@var{c}} @cindex hat notation for control characters Echo control characters in hat notation (@samp{^@var{c}}) instead of literally. Non-POSIX. May be negated. @item echoke @itemx crtkill @opindex echoke @opindex crtkill Echo the @code{kill} special character by erasing each character on the line as indicated by the @code{echoprt} and @code{echoe} settings, instead of by the @code{echoctl} and @code{echok} settings. Non-POSIX. May be negated. @end table @node Combination @subsection Combination settings @cindex combination settings Combination settings: @table @samp @item evenp @opindex evenp @itemx parity @opindex parity Same as @code{parenb -parodd cs7}. May be negated. If negated, same as @code{-parenb cs8}. @item oddp @opindex oddp Same as @code{parenb parodd cs7}. May be negated. If negated, same as @code{-parenb cs8}. @item nl @opindex nl Same as @code{-icrnl -onlcr}. May be negated. If negated, same as @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}. @item ek @opindex ek Reset the @code{erase} and @code{kill} special characters to their default values. @item sane @opindex sane Same as: @c This is too long to write inline. @example cread -ignbrk brkint -inlcr -igncr icrnl -ixoff -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke @end example @noindent and also sets all special characters to their default values. @item cooked @opindex cooked Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus sets the @code{eof} and @code{eol} characters to their default values if they are the same as the @code{min} and @code{time} characters. May be negated. If negated, same as @code{raw}. @item raw @opindex raw Same as: @example -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -opost -isig -icanon -xcase min 1 time 0 @end example @noindent May be negated. If negated, same as @code{cooked}. @item cbreak @opindex cbreak Same as @code{-icanon}. May be negated. If negated, same as @code{icanon}. @item pass8 @opindex pass8 @cindex eight-bit characters Same as @code{-parenb -istrip cs8}. May be negated. If negated, same as @code{parenb istrip cs7}. @item litout @opindex litout Same as @code{-parenb -istrip -opost cs8}. May be negated. If negated, same as @code{parenb istrip opost cs7}. @item decctlq @opindex decctlq Same as @code{-ixany}. Non-POSIX. May be negated. @item tabs @opindex tabs Same as @code{tab0}. Non-POSIX. May be negated. If negated, same as @code{tab3}. @item lcase @itemx LCASE @opindex lcase @opindex LCASE Same as @code{xcase iuclc olcuc}. Non-POSIX. May be negated. @item crt @opindex crt Same as @code{echoe echoctl echoke}. @item dec @opindex dec Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}. @end table @node Characters @subsection Special characters @cindex special characters @cindex characters, special The special characters' default values vary from system to system. They are set with the syntax @samp{name value}, where the names are listed below and the value can be given either literally, in hat notation (@samp{^@var{c}}), or as an integer which may start with @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or any other digit to indicate decimal. @cindex disabling special characters @kindex u@r{, and disabling special characters} For GNU stty, giving a value of @code{^-} or @code{undef} disables that special character. (This is incompatible with Ultrix @code{stty}, which uses a value of @samp{u} to disable a special character. GNU @code{stty} treats a value @samp{u} like any other, namely to set that special character to @key{u}.) @table @samp @item intr @opindex intr Send an interrupt signal. @item quit @opindex quit Send a quit signal. @item erase @opindex erase Erase the last character typed. @item kill @opindex kill Erase the current line. @item eof @opindex eof Send an end of file (terminate the input). @item eol @opindex eol End the line. @item eol2 @opindex eol2 Alternate character to end the line. Non-POSIX. @item swtch @opindex swtch Switch to a different shell layer. Non-POSIX. @item start @opindex start Restart the output after stopping it. @item stop @opindex stop Stop the output. @item susp @opindex susp Send a terminal stop signal. @item dsusp @opindex dsusp Send a terminal stop signal after flushing the input. Non-POSIX. @item rprnt @opindex rprnt Redraw the current line. Non-POSIX. @item werase @opindex werase Erase the last word typed. Non-POSIX. @item lnext @opindex lnext Enter the next character typed literally, even if it is a special character. Non-POSIX. @end table @node Special @subsection Special settings @cindex special settings @table @samp @item min @var{n} @opindex min Set the minimum number of characters that will satisfy a read until the time value has expired, when @code{-icanon} is set. @item time @var{n} @opindex time Set the number of tenths of a second before reads time out if the min number of characters have not been read, when @code{-icanon} is set. @item ispeed @var{n} @opindex ispeed Set the input speed to @var{n}. @item ospeed @var{n} @opindex ospeed Set the output speed to @var{n}. @item rows @var{n} @opindex rows Tell the tty kernel driver that the terminal has @var{n} rows. Non-POSIX. @item cols @var{n} @itemx columns @var{n} @opindex cols @opindex columns Tell the kernel that the terminal has @var{n} columns. Non-POSIX. @item size @opindex size @vindex LINES @vindex COLUMNS Print the number of rows and columns that the kernel thinks the terminal has. (Systems that don't support rows and cols in the kernel typically use the environment variables @code{LINES} and @code{COLUMNS} instead; however, GNU @code{stty} does not know anything about them.) Non-POSIX. @item line @var{n} @opindex line Use line discipline @var{n}. Non-POSIX. @item speed @opindex speed Print the terminal speed. @item @var{n} @cindex baud rate, setting Set the input and output speeds to @var{n}. @var{n} can be one of: 0 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200; @code{extb} is the same as 38400. 0 hangs up the line if @code{-clocal} is set. @end table @node printenv invocation @section @code{printenv}: Print all or some environment variables @pindex printenv @cindex printing all or some environment variables @cindex environment variables, printing Synopsis: @example printenv [@var{option}] [@var{variable}]@dots{} @end example If no @var{variable}s are specified, @code{printenv} prints the value of every environment variable. Otherwise, it prints the value of each @var{variable} that is set, and nothing for those that are not set. The only options are a lone @samp{--help} or @samp{--version}. @xref{Common options}. @cindex exit status of @code{printenv} Exit status: @display 0 if all variables specified were found 1 if at least one specified variable was not found 2 if a write error occurred @end display @node tty invocation @section @code{tty}: Print file name of terminal on standard input @pindex tty @cindex print terminal file name @cindex terminal file name, printing @code{tty} prints the file name of the tty connected to its standard input. It prints @samp{not a tty} if standard input is not a tty. Synopsis: @example tty [@var{option}]@dots{} @end example The program accepts the following option. Also see @ref{Common options}. @table @samp @item -s @itemx --silent @itemx --quiet @opindex -s @opindex --silent @opindex --quiet Print nothing; only return an exit status. @end table @cindex exit status of @code{tty} Exit status: @display 0 if standard input is a tty 1 if standard input is not a tty 2 if given incorrect arguments 3 if a write error occurs @end display @node User information @chapter User information @cindex user information, commands for @cindex commands for printing user information This section describes commands that print user-related information: logins, groups, and so forth. @menu * id invocation:: Print real and effective uid and gid. * logname invocation:: Print current login name. * whoami invocation:: Print effective user id. * groups invocation:: Print group names a user is in. * users invocation:: Print login names of users currently logged in. * who invocation:: Print who is currently logged in. @end menu @node id invocation @section @code{id}: Print real and effective uid and gid @pindex id @cindex real uid and gid, printing @cindex effective uid and gid, printing @cindex printing real and effective uid and gid @noindent @code{id} prints information about the given user, or the process running it if no user is specified. Synopsis: @example id [@var{option}]@dots{} [@var{username}] @end example By default, it prints the real user id, real group id, effective user id if different from the real user id, effective group id if different from the real group id, and supplemental group ids. Each of these numeric values is preceded by an identifying string and followed by the corresponding user or group name in parentheses. The options cause @code{id} to print only part of the above information. Also see @ref{Common options}. @table @samp @item -g @itemx --group @opindex -g @opindex --group Print only the group id. @item -G @itemx --groups @opindex -G @opindex --groups Print only the supplementary groups. @item -n @itemx --name @opindex -n @opindex --name Print the user or group name instead of the ID number. Requires @code{-u}, @code{-g}, or @code{-G}. @item -r @itemx --real @opindex -r @opindex --real Print the real, instead of effective, user or group id. Requires @code{-u}, @code{-g}, or @code{-G}. @item -u @itemx --user @opindex -u @opindex --user Print only the user id. @end table @node logname invocation @section @code{logname}: Print current login name @pindex logname @cindex printing user's login name @cindex login name, printing @cindex user name, printing @flindex /etc/utmp @flindex utmp @code{logname} prints the calling user's name, as found in the file @file{/etc/utmp}, and exits with a status of 0. If there is no @file{/etc/utmp} entry for the calling process, @code{logname} prints an error message and exits with a status of 1. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node whoami invocation @section @code{whoami}: Print effective user id @pindex whoami @cindex effective UID, printing @cindex printing the effective UID @code{whoami} prints the user name associated with the current effective user id. It is equivalent to the command @samp{id -un}. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node groups invocation @section @code{groups}: Print group names a user is in @pindex groups @cindex printing groups a user is in @cindex supplementary groups, printing @code{groups} prints the names of the primary and any supplementary groups that each given @var{username}, or the current process if none are given, is in. If user names are given, the name of each user is printed before the list of that user's groups. Synopsis: @example groups [@var{username}]@dots{} @end example The group lists are equivalent to the output of the command @samp{id -Gn}. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node users invocation @section @code{users}: Print login names of users currently logged in @pindex users @cindex printing current usernames @cindex usernames, printing current @cindex login sessions, printing users with @code{users} prints on a single line a blank-separated list of user names of users currently logged in to the current host. Each user name corresponds to a login session, so if a user has more than one login session, that user's name will appear the same number of times in the output. Synopsis: @example users [@var{file}] @end example @flindex /etc/utmp @flindex /etc/wtmp With no @var{file} argument, @code{users} extracts its information from the file @file{/etc/utmp}. If a file argument is given, @code{users} uses that file instead. A common choice is @file{/etc/wtmp}. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node who invocation @section @code{who}: Print who is currently logged in @pindex who @cindex printing current user information @cindex information, about current users Synopsis: @example @code{who} [@var{option}] [@var{file}] [am i] @end example @cindex terminal lines, currently used @cindex login time @cindex remote hostname If given no non-option arguments, @code{who} prints the following information for each user currently logged on: login name, terminal line, login time, and remote hostname or X display. @flindex /etc/utmp @flindex /etc/wtmp If given one non-option argument, @code{who} uses that instead of @file{/etc/utmp} as the name of the file containing the record of users logged on. @file{/etc/wtmp} is commonly given as an argument to @code{who} to look at who has previously logged on. @opindex am i @opindex who am i If given two non-option arguments, @code{who} prints only the entry for the user running it (determined from its standard input), preceded by the hostname. Traditionally, the two arguments given are @samp{am i}, as in @samp{who am i}. The program accepts the following options. Also see @ref{Common options}. @table @samp @item -m @opindex -m Same as @samp{who am i}. @item -q @itemx --count @opindex -q @opindex --count Print only the login names and the number of users logged on. Overrides all other options. @item -s @opindex -s Ignored; for compatibility with other versions of @code{who}. @item -i @itemx -u @itemx --idle @opindex -i @opindex -u @opindex --idle @cindex idle time After the login time, print the number of hours and minutes that the user has been idle. @samp{.} means the user was active in last minute. @samp{old} means the user was idle for more than 24 hours. @item -H @itemx --heading @opindex -H @opindex --heading Print a line of column headings. @item -w @itemx -T @itemx --mesg @itemx --message @itemx --writable @opindex -w @opindex -T @opindex --mesg @opindex --message @opindex --writable @cindex message status @pindex write@r{, allowed} After each login name print a character indicating the user's message status: @display @samp{+} allowing @code{write} messages @samp{-} disallowing @code{write} messages @samp{?} cannot find terminal device @end display @end table @node System context @chapter System context @cindex system context @cindex context, system @cindex commands for system context This section describes commands that print or change system-wide information. @menu * date invocation:: Print or set system date and time. * uname invocation:: Print system information. * hostname invocation:: Print or set system name. @end menu @node date invocation @section @code{date}: Print or set system date and time @pindex date @cindex time, printing or setting @cindex printing the current time @code{date} with no arguments prints the current time and date, in the format of the @samp{%c} directive (described below). Synopses: @example date [@var{option}]@dots{} [+@var{format}] date [-u|--utc|--universal] @c this avoids a newline in the output [ @var{MMDDhhmm}[[@var{CC}]@var{YY}][.@var{ss}] ] @end example @findex strftime @r{and @code{date}} @cindex time formats @cindex formatting times If given an argument that starts with a @samp{+}, @code{date} prints the current time and date (or the time and date specified by the @code{--date} option, see below) in the format defined by that argument, which is the same as in the @code{strftime} function. Except for directives, which start with @samp{%}, characters in the format string are printed unchanged. The directives are described below. @menu * Time directives:: %[HIklMprsSTXZ] * Date directives:: %[aAbBcdDhjmUwWxyY] * Literal directives:: %[%nt] * Padding:: Pad with zeroes, spaces (%_), or nothing (%-). * Setting the time:: Changing the system clock. * Options for date:: Instead of the current time. * Examples of date:: Examples. @end menu @node Time directives @subsection Time directives @cindex time directives @cindex directives, time @code{date} directives related to times. @table @samp @item %H hour (00@dots{}23) @item %I hour (01@dots{}12) @item %k hour ( 0@dots{}23) @item %l hour ( 1@dots{}12) @item %M minute (00@dots{}59) @item %p locale's AM or PM @item %r time, 12-hour (hh:mm:ss [AP]M) @item %s @cindex epoch, seconds since @cindex seconds since the epoch @cindex beginning of time seconds since the epoch, i.e., 1 January 1970 00:00:00 UTC (a GNU extension) @item %S second (00@dots{}61) @item %T time, 24-hour (hh:mm:ss) @item %X locale's time representation (%H:%M:%S) @item %Z timezone (e.g., EDT), or nothing if no timezone is determinable @end table @node Date directives @subsection Date directives @cindex date directives @cindex directives, date @code{date} directives related to dates. @table @samp @item %a locale's abbreviated weekday name (Sun@dots{}Sat) @item %A locale's full weekday name, variable length (Sunday@dots{}Saturday) @item %b locale's abbreviated month name (Jan@dots{}Dec) @item %B locale's full month name, variable length (January@dots{}December) @item %c locale's date and time (Sat Nov 04 12:02:33 EST 1989) @item %d day of month (01@dots{}31) @item %D date (mm/dd/yy) @item %h same as %b @item %j day of year (001@dots{}366) @item %m month (01@dots{}12) @item %U week number of year with Sunday as first day of week (00@dots{}53) @item %w day of week (0@dots{}6) with 0 corresponding to Sunday @item %W week number of year with Monday as first day of week (00@dots{}53) @item %x locale's date representation (mm/dd/yy) @item %y last two digits of year (00@dots{}99) @item %Y year (1970@dots{}.) @end table @node Literal directives @subsection Literal directives @cindex literal directives @cindex directives, literal @code{date} directives that produce literal strings. @table @samp @item %% a literal % @item %n a newline @item %t a horizontal tab @end table @node Padding @subsection Padding @cindex numeric field padding @cindex padding of numeric fields @cindex fields, padding numeric By default, @code{date} pads numeric fields with zeroes, so that, for example, numeric months are always output as two digits. GNU @code{date} recognizes the following numeric modifiers between the @samp{%} and the directive. @table @samp @item - (hyphen) do not pad the field; useful if the output is intended for human consumption. @item _ (underscore) pad the field with spaces; useful if you need a fixed number of characters in the output, but zeroes are too distracting. @end table @noindent These are GNU extensions. Here is an example illustrating the differences: @example date +%d/%m -d "Feb 1" @result{} 01/02 date +%-d/%-m -d "Feb 1" @result{} 1/2 date +%_d/%_m -d "Feb 1" @result{} 1/ 2 @end example @node Setting the time @subsection Setting the time @cindex setting the time @cindex time setting @cindex appropriate privileges If given an argument that does not start with @samp{+}, @code{date} sets the system clock to the time and date specified by that argument (as described below). You must have appropriate privileges to set the system clock. The @samp{--date} and @samp{--set} options may not be used with such an argument. The @samp{--universal} option may be used with such an argument to indicate that the specified time and date are relative to Coordinated Universal Time rather than to the local time zone. The argument must consist entirely of digits, which have the following meaning: @table @var @item MM month @item DD day within month @item hh hour @item mm minute @item CC first two digits of year (optional) @item YY last two digits of year (optional) @item ss second (optional) @end table The @samp{--set} option also sets the system clock; see the next section. @node Options for date @subsection Options for @code{date} @cindex @code{date} options @cindex options for @code{date} The program accepts the following options. Also see @ref{Common options}. @table @samp @item -d @var{datestr} @itemx --date=@var{datestr} @opindex -d @opindex --date @cindex parsing date strings @cindex date strings, parsing @cindex arbitrary date strings, parsing @opindex yesterday @opindex tomorrow @opindex next @var{day} @opindex last @var{day} Display the time and date specified in @var{datestr} instead of the current time and date. @var{datestr} can be in almost any common format. It can contain month names, timezones, @samp{am} and @samp{pm}, @samp{yesterday}, @samp{ago}, @samp{next}, etc. @xref{Date input formats}. @item -r @var{file} @itemx --reference=@var{file} @opindex -r @opindex --reference Display the time and date as obtained from a reference @var{file}, instead of the current time and date. Each file has a few timestamps associated with it. In this context, the time and date of the last modification are used. @item -f @var{datefile} @itemx --file=@var{datefile} @opindex -f @opindex --file Parse each line in @var{datefile} as with @samp{-d} and display the resulting time and date. If @var{datefile} is @samp{-}, use standard input. This is useful when you have many dates to process, because the system overhead of starting up the @code{date} executable many times can be considerable. @item -s @var{datestr} @itemx --set=@var{datestr} @opindex -s @opindex --set Set the time and date to @var{datestr}, See @samp{-d} above. @item -u @itemx --utc @itemx --universal @opindex -u @opindex --utc @opindex --universal @cindex coordinated universal time @cindex Greenwich Mean Time Print or set the time and date in Universal Coordinated Time instead of in local (wall clock) time. @end table @node Examples of date @subsection Examples of @code{date} @cindex examples of @code{date} Here are a few examples. Also see the documentation for the @samp{-d} option in the previous section. @itemize @bullet @item To print the date of the day before yesterday: @example date --date='2 days ago' @end example @item To print the date of the day three months and one day hence: @example date --date='3 months 1 day' @end example @item To print the day of year of Christmas in the current year: @example date --date='25 Dec' +%j @end example @item To print the current full month name and the day of the month: @example date '+%B %d' @end example But this may not be what you want because for the first nine days of the month, the @samp{%d} expands to a zero-padded two-digit field, for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}. @item To print a date without the leading zero for one-digit days of the month, you can use the (GNU extension) @code{-} modifier to suppress the padding altogether. @example date -d=1may '+%B %-d' @end example @item To print the current date and time in the format required by many non-GNU versions of @code{date} when setting the system clock: @example date +%m%d%H%M%Y.%S @end example @item To set the system clock forward by two minutes: @example date --set='+2 minutes' @end example @end itemize @node uname invocation @section @code{uname}: Print system information @pindex uname @cindex print system information @cindex system information, printing @code{uname} prints information about the machine and operating system it is run on. If no options are given, @code{uname} acts as if the @code{-s} option were given. Synopsis: @example uname [@var{option}]@dots{} @end example If multiple options or @code{-a} are given, the selected information is printed in this order: @example @var{sysname} @var{nodename} @var{release} @var{osversion} @var{machine} @end example The @var{osversion}, at least, may well be multiple words. For example: @example uname -a @result{} Linux hayley 1.0.4 #3 Thu May 12 18:06:34 1994 i486 @end example The program accepts the following options. Also see @ref{Common options}. @table @samp @item -a @itemx --all @opindex -a @opindex --all Print all of the below information. @item -m @itemx --machine @opindex -m @opindex --machine @cindex machine type @cindex hardware type Print the machine (hardware) type. @item -n @itemx --nodename @opindex -n @opindex --nodename @cindex hostname @cindex node name @cindex network node name Print the machine's network node hostname. @item -r @itemx --release @opindex -r @opindex --release @cindex operating system release @cindex release of operating system Print the operating system release. @item -s @itemx --sysname @opindex -s @opindex --sysname @cindex operating system name @cindex name of operating system Print the operating system name. @item -v @opindex -v @cindex operating system version @cindex version of operating system Print the operating system version. @end table @node hostname invocation @section @code{hostname}: Print or set system name @pindex hostname @cindex setting the hostname @cindex printing the hostname @cindex system name, printing @cindex appropriate privileges With no arguments, @code{hostname} prints the name of the current host system. With one argument, it sets the current host name to the specified string. You must have appropriate privileges to set the host name. Synopsis: @example hostname [@var{name}] @end example The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node Modified command invocation @chapter Modified command invocation @cindex modified command invocation @cindex invocation of commands, modified @cindex commands for invoking other commands This section describes commands that run other commands in some context different than the current one: a modified environment, as a different user, etc. @menu * env invocation:: Modify environment variables. * nice invocation:: Modify scheduling priority. * nohup invocation:: Immunize to hangups. * su invocation:: Modify user and group id. @end menu @node env invocation @section @code{env}: Run a command in a modified environment @pindex env @cindex environment, running a program in a modified @cindex modified environment, running a program in @code{env} runs a command with an environment modified as specified by the command line arguments. Synopses: @example env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c [@var{command} [@var{args}]@dots{}] env @end example Arguments of the form @samp{@var{variable}=@var{value}} set the environment variable @var{variable} to value @var{value}. @var{value} may be empty (@samp{@var{variable}=}). Setting a variable to an empty value is different from unsetting it. @vindex PATH The first remaining argument specifies the program name to invoke; it is searched for according to the @code{PATH} environment variable. Any remaining arguments are passed as arguments to that program. @cindex environment, printing If no command name is specified following the environment specifications, the resulting environment is printed. This is like specifying a command name of @code{printenv}. The program accepts the following options. Also see @ref{Common options}. @table @samp @item -u @var{name} @itemx --unset=@var{name} @opindex -u @opindex -unset Remove variable @var{name} from the environment, if it was in the environment. @item - @itemx -i @itemx --ignore-environment @opindex - @opindex -i @opindex --ignore-environment Start with an empty environment, ignoring the inherited environment. @end table @node nice invocation @section @code{nice}: Run a command with modified scheduling priority @pindex nice @cindex modifying scheduling priority @cindex scheduling priority, modifying @cindex priority, modifying @cindex appropriate privileges If no arguments are given, @code{nice} prints the current scheduling priority, which it inherited. Otherwise, @code{nice} runs the given @var{command} with its scheduling priority adjusted. If no @var{adjustment} is given, the priority of the command is incremented by 10. You must have appropriate privileges to specify a negative adjustment. The priority can be adjusted by @code{nice} over the range of -20 (the highest priority) to 19 (the lowest). Synopsis: @example nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}] @end example @cindex conflicts with shell built-ins @cindex built-in shell commands, conflicts with Because most shells have a built-in command by the same name, using the unadorned command name in a script or interactively may get you different functionality than that described here. The program accepts the following option. Also see @ref{Common options}. @table @samp @item -n @var{adjustment} @itemx -@var{adjustment} @itemx --adjustment=@var{adjustment} @opindex -n @opindex --adjustment @opindex -@var{adjustment} Add @var{adjustment} instead of 10 to the command's priority. @end table @node nohup invocation @section @code{nohup}: Run a command immune to hangups @pindex nohup @cindex hangups, immunity to @cindex immunity to hangups @flindex nohup.out @code{nohup} runs the given @var{command} with hangup signals ignored, so that the command can continue running in the background after you log out. Synopsis: @example nohup @var{command} [@var{arg}]@dots{} @end example @flindex nohup.out Also, the scheduling priority is increased by 5. If standard output is a tty, it and standard error are redirected so that they are appended to the file @file{nohup.out}; if that cannot be written to, they are appended to the file @file{$HOME/nohup.out}. If that cannot be written to, the command is not run. If @code{nohup} creates either @file{nohup.out} or @file{$HOME/nohup.out}, it creates it with no ``group'' or ``other'' access permissions. It does not change the permissions if the output file already existed. @code{nohup} does not automatically put the command it runs in the background; you must do that explicitly, by ending the command line with an @samp{&}. The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node su invocation @section @code{su}: Run a command with substitute user and group id @pindex su @cindex substitute user and group ids @cindex user id, switching @cindex super-user, becoming @cindex root, becoming @code{su} allows one user to temporarily become another user. It runs a command (often an interactive shell) with the real and effective user id, group id, and supplemental groups of a given @var{user}. Synopsis: @example su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}] @end example @cindex passwd entry, and @code{su} shell @flindex /bin/sh @flindex /etc/passwd If no @var{user} is given, the default is @code{root}, the super-user. The shell to use is taken from @var{user}'s @code{passwd} entry, or @file{/bin/sh} if none is specified there. If @var{user} has a password, @code{su} prompts for the password unless run by a user with effective user id of zero (the super-user). @vindex HOME @vindex SHELL @vindex USER @vindex LOGNAME @cindex login shell By default, @code{su} does not change the current directory. It sets the environment variables @code{HOME} and @code{SHELL} from the password entry for @var{user}, and if @var{user} is not the super-user, sets @code{USER} and @code{LOGNAME} to @var{user}. By default, the shell is not a login shell. Any additional @var{arg}s are passed as additional arguments to the shell. @cindex @samp{-su} GNU @code{su} does not treat @file{/bin/sh} or any other shells specially (e.g., by setting @code{argv[0]} to @samp{-su}, passing @code{-c} only to certain shells, etc.). @findex syslog @code{su} can optionally be compiled to use @code{syslog} to report failed, and optionally successful, @code{su} attempts. (If the system supports @code{syslog}.) However, GNU @code{su} does not check if the user is a member of the @code{wheel} group; see below. The program accepts the following options. Also see @ref{Common options}. @table @samp @item -c @var{command} @itemx --command=@var{command} @opindex -c @opindex --command Pass @var{command}, a single command line to run, to the shell with a @code{-c} option instead of starting an interactive shell. @item -f @itemx --fast @opindex -f @opindex --fast @flindex .cshrc @cindex file name pattern expansion, disabled @cindex globbing, disabled Pass the @code{-f} option to the shell. This probably only makes sense if the shell run is @code{csh} or @code{tcsh}, for which the @code{-f} option prevents reading the startup file (@file{.cshrc}). With Bourne-like shells, the @code{-f} option disables file name pattern expansion (globbing), which is not likely to be useful. @item - @itemx -l @itemx --login @opindex - @opindex -l @opindex --login @c other variables already indexed above @vindex TERM @vindex PATH @cindex login shell, creating Make the shell a login shell. This means the following. Unset all environment variables except @code{TERM}, @code{HOME}, and @code{SHELL} (which are set as described above), and @code{USER} and @code{LOGNAME} (which are set, even for the super-user, as described above), and set @code{PATH} to a compiled-in default value. Change to @var{user}'s home directory. Prepend @samp{-} to the shell's name, intended to make it read its login startup file(s). @item -m @itemx -p @itemx --preserve-environment @opindex -m @opindex -p @opindex --preserve-environment @cindex environment, preserving @flindex /etc/shells @cindex restricted shell Do not change the environment variables @code{HOME}, @code{USER}, @code{LOGNAME}, or @code{SHELL}. Run the shell given in the environment variable @code{SHELL} instead of the shell from @var{user}'s passwd entry, unless the user running @code{su} is not the superuser and @var{user}'s shell is restricted. A @dfn{restricted shell} is one that is not listed in the file @file{/etc/shells}, or in a compiled-in list if that file does not exist. Parts of what this option does can be overridden by @code{--login} and @code{--shell}. @item -s @var{shell} @itemx --shell=@var{shell} @opindex -s @opindex --shell Run @var{shell} instead of the shell from @var{user}'s passwd entry, unless the user running @code{su} is not the superuser and @var{user}'s shell is restricted (see @samp{-m} just above). @end table @cindex wheel group, not supported @cindex group wheel, not supported @cindex fascism @heading Why GNU @code{su} does not support the @samp{wheel} group (This section is by Richard Stallman.) @cindex Twenex @cindex MIT AI lab Sometimes a few of the users try to hold total power over all the rest. For example, in 1984, a few users at the MIT AI lab decided to seize power by changing the operator password on the Twenex system and keeping it secret from everyone else. (I was able to thwart this coup and give power back to the users by patching the kernel, but I wouldn't know how to do that in Unix.) However, occasionally the rulers do tell someone. Under the usual @code{su} mechanism, once someone learns the root password who sympathizes with the ordinary users, he or she can tell the rest. The ``wheel group'' feature would make this impossible, and thus cement the power of the rulers. I'm on the side of the masses, not that of the rulers. If you are used to supporting the bosses and sysadmins in whatever they do, you might find this idea strange at first. @node Delaying @chapter Delaying @cindex delaying commands @cindex commands for delaying Perhaps @code{wait} or other commands should be described here also? @menu * sleep invocation:: Delay for a specified time. @end menu @node sleep invocation @section @code{sleep}: Delay for a specified time @pindex sleep @cindex delay for a specified time @code{sleep} pauses for an amount of time specified by the sum of the values of the command line arguments. Synopsis: @example sleep [@var{number}[smhd]]@dots{} @end example @cindex time units Each argument is a number followed by an optional unit; the default is seconds. The units are: @table @samp @item s seconds @item m minutes @item h hours @item d days @end table The only options are @samp{--help} and @samp{--version}. @xref{Common options}. @node Index @unnumbered Index @printindex cp @contents @bye @c Local variables: @c texinfo-column-for-description: 33 @c End: