GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
Unix |
Unix v7 |
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expr(1) |
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expr − evaluate arguments as an expression
expr arg ...
The arguments are taken as an expression. After evaluation, the result is written on the standard output. Each token of the expression is a separate argument.
The operators
and keywords are listed below. The list is in order of
increasing precedence, with equal precedence operators
grouped.
expr | expr
yields the first expr if it is neither null nor ’0’, otherwise yields the second expr.
expr & expr
yields the first expr if neither expr is null or ’0’, otherwise yields ’0’.
expr relop expr
where relop is one of < <= = != >= >, yields ’1’ if the indicated comparison is true, ’0’ if false. The comparison is numeric if both expr are integers, otherwise lexicographic.
expr + expr
expr - expr
addition or subtraction of the arguments.
expr * expr
expr / expr
expr % expr
multiplication, division, or remainder of the arguments.
expr : expr
The matching operator compares the string first argument with the regular expression second argument; regular expression syntax is the same as that of ed(1). The \(...\) pattern symbols can be used to select a portion of the first argument. Otherwise, the matching operator yields the number of characters matched (’0’ on failure).
( expr )
parentheses for grouping.
Examples:
To add 1 to the Shell variable a:
a=`expr $a + 1`
To find the filename part (least significant part) of the pathname stored in variable a, which may or may not contain ’/’:
expr $a : ´.*/\(.*\)´ ´|´ $a
Note the quoted Shell metacharacters.
ed(1), sh(1), test(1)
Expr returns the following exit codes:
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0 |
if the expression is neither null nor ’0’, | ||
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1 |
if the expression is null or ’0’, | ||
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2 |
for invalid expressions. |
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expr(1) | |