- Expr
expr is a command line
Unix utility which evaluates an expression and outputs the corresponding value.Syntax: expr "(expression)"
"expr" evaluates
integer or string expressions, including pattern matchingregular 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 ">" 8outputs "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]
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