expr - evaluate expression
expr expression
The expr utility evaluates expression and writes the result on standard output.
All operators are separate arguments to the expr utility. Characters special to the command interpreter must be escaped.
Operators are listed below in order of increasing precedence. Operators with equal precedence are grouped within { } symbols.
Returns the evaluation of expr1 if it is neither an empty string nor zero; otherwise, returns the evaluation of expr2.
Returns the evaluation of expr1 if neither expression evaluates to an empty string or zero; otherwise, returns zero.
Returns the results of integer comparison if both arguments are integers; otherwise, returns the results of string comparison us- ing the locale-specific collation sequence. The result of each comparison is 1 if the specified relation is true, or 0 if the relation is false.
Returns the results of addition or subtraction of integer-valued arguments.
Returns the results of multiplication, integer division, or re- mainder of integer-valued arguments.
The ``:'' operator matches expr1 against expr2, which must be a regular expression. The regular expression is anchored to the beginning of the string with an implicit ``^''. The regular expression language is perlre(1).
If the match succeeds and the pattern contains at least one regu- lar expression subexpression ``(...)'', the string correspond- ing to ``$1'' is returned; otherwise the matching operator re- turns the number of characters matched. If the match fails and the pattern contains a regular expression subexpression the null string is returned; otherwise 0.
Parentheses are used for grouping in the usual manner.
a=`expr $a + 1`
expr //$a : '.*/\(.*\)'
expr $a : '.*'
The expr utility exits with one of the following values:
0 the expression is neither an empty string nor 0. 1 the expression is an empty string or 0. 2 the expression is invalid.
The expr utility conforms to IEEE Std1003.2 (``POSIX.2'').