expr(1) expr(1)
NAME
expr - evaluate arguments as an expression
SYNOPSIS
expr arguments
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 0 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, 2s
complement numbers. The length of the expression is limited
to 512 characters. Expressions may be grouped using (escaped)
parentheses.
The operators and keywords are listed below. Characters that
need to be escaped in the shell [see sh(1)] are preceded by \.
The list is in order of increasing precedence, with equal
precedence operators grouped within {} symbols.
expr \| expr
Return the first expr if it is neither null nor 0,
otherwise return the second expr.
expr \& expr
Return the first expr if neither expr is null or 0,
otherwise return 0.
expr { =, \>, \>=, \<, \<=, != } expr
Return the result of an integer comparison if both
arguments are integers, otherwise return the result of a
lexical comparison.
expr { +, - } expr
Add or subtract integer-valued arguments.
expr { \*, /, % } expr
Multiply, divide, or compute remainder of integer-valued
arguments.
Copyright 1994 Novell, Inc. Page 1
expr(1) expr(1)
expr : expr
match expr expr
Compare the first argument with the second argument,
which must be a regular expression. Regular expression
syntax is the same as that of ed(1), except that all
patterns are ``anchored'' (that is, begin with ^) and,
therefore, ^ is not a special character, in that
context. Normally, the matching operator returns the
number of characters matched (0 on failure).
Alternatively, the \( . . . \) pattern symbols can be
used to return a portion of the first argument.
length string
Return the length of string.
substr string index count
Return the portion of string composed of at most count
characters starting at the character position of string
as expressed by index (where the first character of
string is index 1, not 0).
index string character_sequence
Return the index of the first character in string that
is also in character_sequence or 0 to indicate no match.
expr processes supplementary code set characters according to
the locale specified in the LC_CTYPE environment variable [see
LANG on environ(5)]. In regular expressions, pattern searches
are performed on characters, not bytes, as described on ed(1).
String comparisons are affected by the LC_COLLATE and LC_CTYPE
environment variables [see LANG on environ(5)].
Errors
As a side effect of expression evaluation, expr returns the
following exit values:
0 The expression is neither null nor 0.
1 The expression is null or 0.
2 An expression is invalid.
non-numeric argument arithmetic attempted on a non-
numeric string
FILES
/usr/lib/locale/locale/LC_MESSAGES/uxcore.abi
language-specific message file [See LANG on environ(5).]
Copyright 1994 Novell, Inc. Page 2
expr(1) expr(1)
USAGE
Examples
Add 1 to the shell variable a:
a=`expr $a + 1`
The following example emulates basename(1); it returns the
last segment of the path name $a. For $a equal to either
/usr/abc/file or just file, the example returns file. The //
characters eliminate any ambiguity about the division
operator.
expr //$a : '.*/\(.*\)'
NOTICES
After argument processing by the shell, expr cannot tell the
difference between an operator and an operand except by the
value. If $a is an =, the command:
expr $a = '='
looks like:
expr = = =
as the arguments are passed to expr (and they are all taken as
the = operator). The following works:
expr X$a = X=
Copyright 1994 Novell, Inc. Page 3