V10/man/man1/expr.1

.TH EXPR 1
.CT 1 shell 
.SH NAME
expr \- integer and string-match expression evaluator for shell scripts
.SH SYNOPSIS
.B expr
.I arg ...
.SH DESCRIPTION
The arguments are taken as an expression.
After evaluation, the result is written on the standard output.
Each token of the expression is a separate argument.
.PP
The operators and keywords are listed below
in order of increasing precedence,
with equal precedence operators grouped.
.TP \w'\f5(\fI\ expr\ \f5)\ 'u
.IB expr1 " | " expr2
Value is the value of
.I expr1
if that is neither empty nor 0,
otherwise the value of 
.IR expr2.
.TP
.IB expr1 " & " expr2
Value is the value of
.I expr1
if neither
.I expr1
nor
.I expr2
is empty or 0, otherwise 0.
.TP
.I expr1 relop expr2
.I Relop
is one of
.L "< <= = != >= >" .
Value is 1
if the indicated comparison is true, 0
if false.
The comparison is numeric if both
.I expr
are integers, otherwise lexicographic.
.TP
.IB expr1 " + " expr2
.br
.ns
.TP
.IB expr1 " - " expr2
.br
Value is the sum or difference of the (integer) values of 
.I expr1
and
.I expr2.
.TP
.IB expr1 " * " expr2
.br
.ns
.TP
.IB expr1 " / " expr2
.br
.ns
.TP
.IB expr1 " % " expr2
.br
Value is the product, quotient, or remainder of the (integer)
values of 
.I expr1
and
.I expr2.
.TP
.IB expr " : " regexp
Match the string value of 
.I expr
with the regular expression 
.IR regexp ;
regular expression syntax is the same as in
.IR ed (1),
but matches are anchored at the left.
On success a subexpression
.BR \e(\| ... \|\e) ,
if present in
.I regexp,
picks out a return value from the matched string.
Otherwise,
the matching operator yields the number of characters matched
(0 on failure).
.TP
.BI ( " expr " )
Parentheses for grouping.
.TP
.I arg
Value is the string
.I arg.
.PP
.SH EXAMPLES
.TP
.L
a=`expr $a + 1`
Add 1 to shell variable
.IR a .
.TP
.L
expr $a : '.*/\e(.*\e)' '|' $a
Same as
.LR "basename $a" .
.SH "SEE ALSO"
.IR sh (1), 
.IR test (1)
.SH DIAGNOSTICS
.I Expr
returns exit code 0 if the expression is neither null nor 0,
1 if the expression is null or 0, 2 for invalid expressions.