Expr
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{{lowercase|title=expr}}
'''expr''' is a [[command line interface|command line]] [[Unix]] utility which evaluates an [[expression (mathematics)|expression]] and outputs the corresponding value.
Syntax: expr ''(expression)''
''expr'' evaluates [[integer]] or [[String (computer science)|string]] expressions, including pattern matching [[regular expression]]s. Most of the challenge posed in writing expressions is preventing the command line shell from acting on characters intended for ''expr'' to process.
The operators available
* for integers: addition, subtraction, multiplication, division and modulus
* for strings: find substring, find regular expression, find a set of characters in a string, length of string
* for either: comparison (equal, not equal, less than, etc.)
Also, [[boolean]] expressions involving ''and'' and ''or'', such as
expr length "abcdef" "<" 5 "|" 15 - 4 ">" 8
outputs "1". This is because length "abcdef" is 6, which is not less than 5 (so the left side of the | returns zero). But 15 minus 4 is 11 and is greater than 8, so the right side is true, which makes the ''or'' true, so 1 is the result. The program exit status is zero for this example.
== External links ==
*[http://www.linuxmanpages.com/man1/expr.1.php The program's manpage]
*[http://www.gnu.org/software/coreutils/manual/html_node/expr-invocation.html#expr-invocation expr invocation in GNU coreutils manual]
{{Unix commands}}
{{unix-stub}}
[[Category:Unix software]]
[[Category:GNU project software]]
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