expr

expr is a command line Unix utility which evaluates an expression and outputs the corresponding value. It first appeared in Unix v7.

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 invoking 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 regular expression, find a set of characters in a string; in some versions: find substring, length of string
for either: comparison (equal, not equal, less than, etc.)

The following is an 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 length and substr commands is not recommended.

External links

expr: evaluate arguments as an expression – Commands & Utilities Reference, The Single UNIX® Specification, Issue 7 from The Open Group
expr invocation in GNU coreutils manual

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir size split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history id logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix utilities

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