expr

expr
Example of `expr` command that does basic summation
Original authors	Dick Haight (AT&T Bell Laboratories)
Developers	Various open-source and commercial developers
Release	1979; 47 years ago (1979)
Operating system	Unix, Unix-like, IBM i
Platform	Cross-platform
Type	Command

expr is a shell command that evaluates an expression and outputs the result. It evaluates integer or string expressions, including pattern matching regular expressions. Comparison operators (equal, not equal, less than, etc.) apply to both integer and string values. Integer-specific operations include addition, subtraction, multiplication, division and modulus. String-specific operators include:

matching a regular expression (match, or the colon syntax "str" : "reg" for an arbitrary string "str" and regular expression "reg")
finding a set of characters in a string (index)
finding a substring (substr)
finding the length of a string (length)

Each symbol (operator, value, etc.) in the expression must be given as a separate parameter. A common challenge with using the command is preventing the shell from acting on input indented to be the expression as something other than expression.

Originally developed for Unix v7 and standardized by POSIX, the command is available on IBM i,^[1] and for Windows via UnxUtils.^[2]^[3]

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.

Portability

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.

References

↑ IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Archived (PDF) from the original on 2020-09-18. Retrieved 2020-09-05.
↑ "Port of the most important GNU utilities to Windows". Archived from the original on 2022-09-07. Retrieved 2026-02-03.
↑ "Native Win32 ports of some GNU utilities". unxutils.sourceforge.net. Archived from the original on 2006-02-09. Retrieved 2026-02-03.

External links

The Wikibook Guide to Unix has a page on the topic of: Commands

expr: evaluate arguments as an expression – Shell and Utilities Reference, The Single UNIX Specification, Version 5 from The Open Group
expr invocation in GNU coreutils manual

v t e Unix command-line utilities and shell builtins
File system	cat chattr chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask
Processes	at bg crontab fg kill nice ps time
User environment	env exit logname mesg talk tput uname who write
Text processing	awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste patch printf read sed sort strings tail tr troff uniq vi wc xargs
Shell builtins	alias cd echo test unset wait
Searching	find grep
Documentation	man
Software development	ar ctags lex make nm strip yacc
Miscellaneous	bc cal dc expr lp od sleep true and false
Categories Standard Unix programs Unix SUS2008 utilities List

v t e GNU Core Utilities command-line interface programs
File system	chcon chmod chown chgrp cksum cp dd df dir dircolors install ln ls mkdir mkfifo mknod mktemp mv realpath rm rmdir shred sync touch truncate vdir
Text utilities	b2sum base32 base64 cat cksum comm csplit cut expand fmt fold head join md5sum nl numfmt od paste ptx pr sha1sum shuf sort split sum tac tail tr tsort unexpand uniq wc
Shell utilities	arch basename chroot date dirname du echo env expr factor false groups hostid id link logname nice nohup nproc pathchk pinky printenv printf pwd readlink runcon seq sleep stat stdbuf stty tee test timeout true tty uname unlink uptime users who whoami yes

This Unix-related article is a stub. You can help Wikipedia by adding missing information.

Example

Portability

See also

References

External links

Related Essays & Commentary

The first post, built on a secure new foundation.

Cargo Cult Science

How to communicate like Him

Earth Microbes Could Survive on the Moon, Raising Contamination Fears Ahead of Artemis