Expr

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The correct title of this article is expr. The initial letter is shown capitalized due to technical restrictions.

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 matching regular expressions. 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 (the backslash escapes a less than from the shell) 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 return value—the program exit status—is zero for this example.)

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