php man page for expr

EXPR(1) 							   User Commands							   EXPR(1)

NAME
       expr - evaluate expressions

SYNOPSIS
       expr EXPRESSION
       expr OPTION

DESCRIPTION
       --help display this help and exit

       --version
	      output version information and exit

       Print the value of EXPRESSION to standard output.  A blank line below separates increasing precedence groups.  EXPRESSION may be:

       ARG1 | ARG2
	      ARG1 if it is neither null nor 0, otherwise ARG2

       ARG1 & ARG2
	      ARG1 if neither argument is null or 0, otherwise 0

       ARG1 < ARG2
	      ARG1 is less than ARG2

       ARG1 <= ARG2
	      ARG1 is less than or equal to ARG2

       ARG1 = ARG2
	      ARG1 is equal to ARG2

       ARG1 != ARG2
	      ARG1 is unequal to ARG2

       ARG1 >= ARG2
	      ARG1 is greater than or equal to ARG2

       ARG1 > ARG2
	      ARG1 is greater than ARG2

       ARG1 + ARG2
	      arithmetic sum of ARG1 and ARG2

       ARG1 - ARG2
	      arithmetic difference of ARG1 and ARG2

       ARG1 * ARG2
	      arithmetic product of ARG1 and ARG2

       ARG1 / ARG2
	      arithmetic quotient of ARG1 divided by ARG2

       ARG1 % ARG2
	      arithmetic remainder of ARG1 divided by ARG2

       STRING : REGEXP
	      anchored pattern match of REGEXP in STRING

       match STRING REGEXP
	      same as STRING : REGEXP

       substr STRING POS LENGTH
	      substring of STRING, POS counted from 1

       index STRING CHARS
	      index in STRING where any CHARS is found, or 0

       length STRING
	      length of STRING

       + TOKEN
	      interpret TOKEN as a string, even if it is a

	      keyword like 'match' or an operator like '/'

       ( EXPRESSION )
	      value of EXPRESSION

       Beware that many operators need to be escaped or quoted for shells.  Comparisons are arithmetic if both ARGs are numbers, else lexicograph-
       ical.  Pattern matches return the string matched between ( and ) or null; if ( and ) are not used, they return the number of characters
       matched or 0.

       Exit  status  is 0 if EXPRESSION is neither null nor 0, 1 if EXPRESSION is null or 0, 2 if EXPRESSION is syntactically invalid, and 3 if an
       error occurred.

AUTHOR
       Written by Mike Parker, James Youngman, and Paul Eggert.

REPORTING BUGS
       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report expr translation bugs to <http://translationproject.org/team/>

COPYRIGHT
       Copyright (C) 2017 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO
       Full documentation at: <http://www.gnu.org/software/coreutils/expr>
       or available locally via: info '(coreutils) expr invocation'

GNU coreutils 8.28						   January 2018 							   EXPR(1)