.TH EXPR 1  "26 March 1984"
.\" @(#)expr.1 1.1 92/07/30 SMI; from UCB 4.1
.SH NAME
expr \- evaluate arguments as an expression
.SH SYNOPSIS
.B expr
arg .\|.\|.
.SH DESCRIPTION
.IX "expr command"  ""  "\fLexpr\fP \(em evaluate expressions"
.IX "expression evaluation"
.IX "evaluate expressions"
.LP
.I Expr
evaluates expressions as specified by its arguments.
Each token of the expression is a separate argument.
After evaluation, the result is written on the standard output.
.LP
The operators and keywords are listed below.
The list is in order of increasing precedence,
with equal precedence operators grouped.
.TP
.I expr | expr
yields the first
.I expr
if it is neither null nor `0', otherwise yields the second
.I expr.
.TP
.I expr & expr
yields the first
.I expr
if neither
.I expr
is null or `0', otherwise yields `0'.
.TP
.I expr relop expr
yields `1' if the indicated comparison is true, `0' if false.  The
comparison is numeric if both
.I expr
are integers, otherwise the comparison is lexicographic.
.I relop
is one of < (less than), <= (less than or equal to), = (equal to),
!= (not equal to), >= (greater than or equal to), and > (greater than).
.TP
.IR expr " + " expr
.br
.ns
.TP
.IR expr " \- " expr
.br
addition or subtraction of the arguments.
.TP
.IR expr " * " expr
.br
.ns
.TP
.IR expr " / " expr
.br
.ns
.TP
.IR expr " % " expr
.br
multiplication, division, or remainder of the arguments.
.TP
.IR expr " : " expr
.br
.ns
.TP
match \fIstring regular-expression\fP
.br
The two forms of the matching operator above are synonymous.  The matching
operator compares the string first argument with the regular expression
second argument; regular expression syntax is the same as that of
.IR ed (1).
The \fB\\(\|.\|.\|.\|\\)\fP pattern symbols can be used to select a portion
of the first argument.  Otherwise, the matching operator yields the number
of characters matched (`0' on failure).
.TP
substr \fIstring integer-1 integer-2\fP
extracts the subtring of 
.I string
starting at position
.I integer-1
and of length
.I integer-2
characters.  If
.I integer-1 has a value greater than the length of
.IR string ,
.I expr
returns a null string.  If 
you try to extract more characters than there are in
.IR string ,
.I expr
returns all the remaining characters from
.IR string .
Beware of using negative values for either
.I integer-1
or
.I integer-2
as 
.I expr
tends to run forever in these cases.
.TP
index \fIstring\fP \fIcharacter-list\fP
reports the first position in
.I string
at which any one of the characters in
.I character-list
matches a character in 
.IR string .
.TP
length \fIstring\fP
returns the length (that is, the number of characters) of
.IR string .
.TP
.RI ( " expr " )
parentheses for grouping.
.SH EXAMPLES
.LP
To add 1 to the Shell variable
.IR a :
.IP
a=\`expr $a + 1\`
.LP
To find the filename part (least significant part)
of the pathname stored in variable
.IR a ,
which may or may not contain `/':
.IP
expr $a : \'.*/\e(\^.*\e)\' \'\^|\' $a
.LP
Note the quoted Shell metacharacters.
.SH "SEE ALSO"
sh(1), test(1)
.SH DIAGNOSTICS
.I Expr
returns the following exit codes:
.LP
	0	if the expression is neither null nor `0',
.br
	1	if the expression
is null or `0',
.br
	2	for invalid expressions.
.SH BUGS
.LP
Note that the
.BR match ,
.BR substr ,
.BR length ,
and
.B index
operators cannot themselves be used as ordinary strings.  That is, the
expression:
.RS
.nf
tutorial% \fBexpr index expurgatorious length\fP
syntax error
tutorial%
.fi
.RE
generates the `syntax error' message as shown instead of the value 1 as
you might expect.