SysIII/usr/src/man/man1/expr.1

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.TH EXPR 1
.SH NAME
expr \- evaluate arguments as an expression
.SH SYNOPSIS
.B expr
arguments
.SH DESCRIPTION
The arguments are taken as an expression.
After evaluation, the result is written on the standard output.
Terms of the expression must be separated by blanks.
Characters special to the shell
must be escaped.
Note that \fB0\fP is returned to indicate a zero value,
rather than the null string.
Strings containing blanks or other special characters should be quoted.
Integer-valued arguments may be preceded by a unary minus sign.
Internally, integers are treated as 32-bit, 2's complement numbers.
.PP
The operators and keywords are listed below.
Characters that need to be escaped are preceded by \f3\\\fP.
The list is in order of increasing precedence,
with equal precedence operators grouped within \f3{\|}\fP symbols.
.TP .5i
\fIexpr \fB\e\^\(bv\fI expr\fR
returns the first
.I expr\^
if it is neither null nor \fB0\fP, otherwise
returns the second
.IR expr .
.TP .5i
\fIexpr \fB\e&\fI expr\fR
returns the first
.I expr\^
if neither
.I expr\^
is null or \fB0\fP, otherwise returns \fB0\fP.
.TP .5i
\fIexpr \fR{ \fB=\fR, \fB\e>\fR, \fB\e>=\fR, \fB\e<\fR, \fB\e<=\fR, \fB!=\fR } \fIexpr\fR
returns the result of an integer comparison if both arguments are integers,
otherwise returns the result of a lexical comparison.
.TP .5i
\fIexpr \fR{ \fB+\fR, \fB\- \fR} \fIexpr\fR
addition or subtraction of integer-valued arguments.
.TP .5i
\fIexpr \fR{ \fB\e\(**\fR, \fB/\fR, \fB% \fR} \fIexpr\fR
multiplication, division, or remainder of the integer-valued arguments.
.TP .5i
\fIexpr\fB : \fIexpr\fR
The matching operator \fB:\fP compares the first argument
with the second argument which must be a regular expression;
regular expression syntax is the same as that of
.IR ed (1),
except that all patterns are ``anchored'' (i.e., begin with \f3^\fP)
and, therefore, \fB^\fP is not a special character, in that context.
Normally,
the matching operator returns the number of characters matched
(\fB0\fP on failure).
Alternatively, the
\fB\\(\|.\|.\|.\|\\)\fP
pattern symbols can be used to return a portion of the
first argument.
.SH EXAMPLES
.TP
1.
a=\*`expr\| $a\| +\| 1\*`
.PP
.RS
.RS
adds 1 to the shell variable
.BR a .
.RE
.RE
.TP
2.
\fB#\fP  \*'For $a equal to either "/usr/abc/file" or just "file"\*'
.br
expr\  $a\  \fB:\fP\  \*'\fB.\fP\(**/\e(\fB.\fP\(**\e)\*'\  \e\^\(bv \ $a
.PP
.RS
.RS
returns
the last segment of a path name
(i.e., \fPfile\fP).
Watch out for \f3/\fP alone as an argument:
.I expr\^
will take it as the division operator
(see
.SM BUGS
below).
.RE
.RE
.ne 6
.TP
3.
\fB#\fP \ A better representation of example 2.
.br
expr\  //$a\  \fB:\fP\  \*'\fB.\fP\(**/\e(\fB.\fP\(**\e)\*'
.PP
.RS
.RS
The addition of the
.B //
characters eliminates any ambiguity about the division operator and simplifies
the whole expression.
.RE
.RE
.TP
4.
expr \ \s-1$VAR\s0 \ \fB:\fP \ \*'\fB.\(**\fP\*'
.PP
.RS
.RS
returns the number of characters in
.SM
.BR $VAR .
.RE
.RE
.SH "SEE ALSO"
ed(1), sh(1).
.SH "EXIT CODE"
As a side effect of expression evaluation,
.I expr\^
returns the following exit values:
.br
	0	if the expression is neither null nor \fB0\fP
.br
	1	if the expression
.I is\^
null or \fB0\fP
.br
	2	for invalid expressions.
.SH DIAGNOSTICS
.PD 0
.TP 1.5i
.I syntax error\^
for operator/operand errors
.TP
.I non-numeric argument\^
if arithmetic is attempted on such a string
.PD
.SH BUGS
After argument processing by the shell,
.I expr\^
cannot tell the difference between an operator and an operand
except by the value.
If
.B $a
is an
.BR = ,
the command:
.PP
	expr \ $a \ = \ \*'=\*'
.PP
looks like:
.PP
	expr \ = \ = \ =
.PP
as the arguments are passed to
.I expr\^
(and they will all be taken as the
.B =
operator).
The following works:
.PP
	expr \ X$a \ = \ X=