expr
Expr-example.png
Example of expr command that does basic summation
Original author(s)Dick Haight
(AT&T Bell Laboratories)
Developer(s)Various open-source and commercial developers
Initial release1979; 43 years ago (1979)
Operating systemUnix, Unix-like, IBM i
PlatformCross-platform
TypeCommand

expr is a command line utility on Unix and Unix-like operating systems which evaluates an expression and outputs the corresponding value. It first appeared in Unix v7. The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.[1] The expr command has also been ported to the IBM i operating system.[2]

Overview

expr evaluates integer or string expressions, including pattern matching regular expressions. Each symbol (operator, value, etc.) in the expression must be given as a separate parameter. Most of the challenge posed in writing expressions is preventing the invoking command line shell from acting on characters intended for expr to process.

Syntax

Syntax: expr expression

The operators available

Example

The following is a (non-POSIX-compliant) example involving boolean expressions:

expr length  "abcdef"  "<"  5  "|"  15  -  4  ">"  8

This example 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.

For pure arithmetic, it is often more convenient to use bc. For example:

echo "3 * 4 + 14 / 2" | bc

since it accepts the expression as a single argument.

For portable shell programming, use of the "index", "length", "match" and "substr" commands must be avoided; string matching remains possible but it must use the "string : regexp" syntax.

See also

References

  1. ^ "Native Win32 ports of some GNU utilities". unxutils.sourceforge.net.
  2. ^ IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). Retrieved 2020-09-05.((cite web)): CS1 maint: url-status (link)