diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/coreutils.texi | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/doc/coreutils.texi b/doc/coreutils.texi index aa309c666..27ed2f675 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -9289,18 +9289,35 @@ True if either @var{expr1} or @var{expr2} is true. @command{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. @command{expr} converts +Operands are either integers or strings. Integers consist of one or +more decimal digits, with an optional leading @samp{-}. +@command{expr} converts 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 @command{expr} itself, though you may need to quote them to protect characters with special meaning to the shell, -e.g., spaces. +e.g., spaces. However, regardless of whether it is quoted, a string +operand should not be a parenthesis or any of @command{expr}'s +operators like @code{+}, so you cannot safely pass an arbitrary string +@code{$str} to expr merely by quoting it to the shell. One way to +work around this is to use the @command{GNU} extension @code{+}, +(e.g., @code{+ "$str" = foo}); a more portable way is to use +@code{@w{" $str"}} and to adjust the rest of the expression to take +the leading space into account (e.g., @code{@w{" $str" = " foo"}}). + +You should not pass a negative integer or a string with leading +@samp{-} as @command{expr}'s first argument, as it might be +misinterpreted as an option; this can be avoided by parenthesization. +Also, portable scripts should not use a string operand that happens to +take the form of an integer; this can be worked around by inserting +leading spaces as mentioned above. @cindex parentheses for grouping Operators may be 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). +may be used for grouping in the usual manner. You must quote +parentheses and many operators to avoid the shell evaluating them, +however. @cindex exit status of @command{expr} Exit status: @@ -9417,7 +9434,7 @@ the connectives (next section) have higher. @kindex - @cindex addition @cindex subtraction -Addition and subtraction. Both arguments are converted to numbers; +Addition and subtraction. Both arguments are converted to integers; an error occurs if this cannot be done. @item * / % @@ -9428,7 +9445,7 @@ an error occurs if this cannot be done. @cindex division @cindex remainder Multiplication, division, remainder. Both arguments are converted to -numbers; an error occurs if this cannot be done. +integers; an error occurs if this cannot be done. @end table @@ -9450,15 +9467,18 @@ are higher precedence than either the string or numeric operators @kindex | @cindex logical or operator @cindex or operator -Returns its first argument if that is neither null nor 0, otherwise its -second argument. +Returns its first argument if that is neither null nor zero, otherwise +its second argument if it is neither null nor zero, otherwise 0. It +does not evaluate its second argument if its first argument is neither +null nor zero. @item & @kindex & @cindex logical and operator @cindex and operator -Return its first argument if neither argument is null or 0, otherwise -0. +Return its first argument if neither argument is null or zero, otherwise +0. It does not evaluate its second argument if its first argument is +null or zero. @item < <= = == != >= > @kindex < @@ -9471,7 +9491,7 @@ Return its first argument if neither argument is null or 0, otherwise @vindex LC_COLLATE Compare the arguments and return 1 if the relation is true, 0 otherwise. @code{==} is a synonym for @code{=}. @command{expr} first tries to convert -both arguments to numbers and do a numeric comparison; if either +both arguments to integers and do a numeric comparison; if either conversion fails, it does a lexicographic comparison using the character collating sequence specified by the @env{LC_COLLATE} locale. |