Ausam/doc/man/man1/expr.1

.th EXPR I 5/31/77
.sh NAME
expr \*- evaluate arguments as an algebraic expression
.sh SYNOPSIS
.bd expr
arg ...
.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,
i.e., `*', `\*v', `&', `(', and `)',
must be escaped.
.s3
The operators and keywords are listed below.
Characters that need to be escaped are preceded by `\\'.
The list is in order of increasing precedence,
with equal precedence operators grouped within `{\|}' symbols.
.s3
.in +3m
.it expr
\\\*|\*v
.it expr
.s3
.it expr
\\&
.it expr
.s3
.it expr
{ +, \*- }
.it expr
.s3
.it expr
{ \\*, /, % }
.it expr
.s3
.bd substr
.it "expr expr expr"
.s3
.bd length
.it expr
.s3
.bd index
.it "expr expr"
.s3
\\(
.it expr
\\)
.s3
.i0
The result of
.it substr
is that portion of the first expression
(possibly null)
which is defined by the offset (second expression, starting at `1') and the
span (third expression).
A large span value can be given to obtain the remainder of the string.
.s3
.it Length
returns the length in characters of the expression that follows.
.s3
.it Index
searches the first expression for the first character
that matches a character from the second expression.
It returns the character position number if it succeeds,
or `0' if it fails.
.s3
The
.it expr
command is handy with Shell variables.
For example:
.s3
.tr ||
	expr substr xxx$a "(" length xxx$a \*- 2 ")" 3 \*v = b
.s3
assigns the last three characters of the
Shell variable
.it $a
into the variable
.it $b.
.s3
Note that `0' is returned to indicate a zero value,
rather than the null string.
Strings containing blanks or other special characters should be quoted.
.sh DIAGNOSTICS
Grumbles from
.it yacc\^\c
(I)
for syntax violations.
.br
"Non-numeric argument" if the argument needs to be, but is not,
an integer.