.\" $OpenBSD: expr.1,v 1.24 2017/08/16 20:10:58 schwarze Exp $ .\" $NetBSD: expr.1,v 1.9 1995/04/28 23:27:13 jtc Exp $ .\" .\" Written by J.T. Conklin <jtc@netbsd.org>. .\" Public domain. .\" .Dd $Mdocdate: August 16 2017 $ .Dt EXPR 1 .Os .Sh NAME .Nm expr .Nd evaluate expression .Sh SYNOPSIS .Nm expr .Ar expression .Sh DESCRIPTION The .Nm utility evaluates .Ar expression and writes the result on standard output. All operators are separate arguments to the .Nm utility. Characters special to the command interpreter must be escaped. .Pp Operators are listed below in order of increasing precedence. Operators with equal precedence are grouped within { } symbols. .Bl -tag -width indent .It Ar expr1 | expr2 Returns the evaluation of .Ar expr1 if it is neither an empty string nor zero; otherwise, returns the evaluation of .Ar expr2 . .It Ar expr1 Li & Ar expr2 Returns the evaluation of .Ar expr1 if neither expression evaluates to an empty string or zero; otherwise, returns zero. .It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2 Returns the results of integer comparison if both arguments are decimal integers; otherwise, returns the results of string comparison using the locale-specific collation sequence. The result of each comparison is 1 if the specified relation is true, or 0 if the relation is false. .It Ar expr1 Li "{+, -}" Ar expr2 Returns the results of addition or subtraction of decimal integer-valued arguments. .It Ar expr1 Li "{*, /, %}" Ar expr2 Returns the results of multiplication, integer division, or remainder of decimal integer-valued arguments. .It Ar expr1 Li \&: Ar expr2 The .Ql \&: operator matches .Ar expr1 against .Ar expr2 , which must be a basic regular expression. The regular expression is anchored to the beginning of the string with an implicit .Ql ^ . .Pp If the match succeeds and the pattern contains at least one regular expression subexpression .Dq "\e(...\e)" , the string corresponding to .Dq "\e1" is returned; otherwise, the matching operator returns the number of characters matched. If the match fails and the pattern contains a regular expression subexpression the null string is returned; otherwise, returns 0. .Pp Note: the empty string cannot be matched using .Bd -literal -offset indent expr '' : '$' .Ed .Pp This is because the returned number of matched characters .Pq zero is indistinguishable from a failed match, so .Nm returns failure .Pq 0 . To match the empty string, use a structure such as: .Bd -literal -offset indent expr X'' : 'X$' .Ed .El .Pp Parentheses are used for grouping in the usual manner. .Sh EXIT STATUS The .Nm utility exits with one of the following values: .Pp .Bl -tag -width Ds -offset indent -compact .It 0 The expression is neither an empty string nor 0. .It 1 The expression is an empty string or 0. .It 2 The expression is invalid. .It \*(Gt2 An error occurred (such as memory allocation failure). .El .Sh EXAMPLES Add 1 to the variable .Va a : .Bd -literal -offset indent $ a=`expr $a + 1` .Ed .Pp Return the filename portion of a pathname stored in variable .Va a . The .Ql // characters act to eliminate ambiguity with the division operator: .Bd -literal -offset indent $ expr "//$a" \&: '.*/\e(.*\e)' .Ed .Pp Return the number of characters in variable .Va a : .Bd -literal -offset indent $ expr $a \&: '.*' .Ed .Sh SEE ALSO .Xr test 1 , .Xr re_format 7 .Sh STANDARDS The .Nm utility is compliant with the .St -p1003.1-2008 specification. .Sh HISTORY The .Nm utility first appeared in the Programmer's Workbench (PWB/UNIX) and has supported regular expressions since .At v7 . It was rewritten from scratch for .Bx 386 0.1 and again for .Nx 1.1 . .Sh AUTHORS .An -nosplit The first free version was written by .An Pace Willisson in 1992. This version was written by .An John T. Conklin in 1994.