EXPR(1) User Commands EXPR(1)
NAME
expr - evaluate arguments as an expression
SYNOPSIS
/usr/bin/expr argument...
/usr/xpg4/bin/expr argument...
/usr/xpg6/bin/expr argument...
DESCRIPTION
/usr/bin/expr, /usr/xpg4/bin/expr The
expr utility evaluates the expression and writes the result to
standard output. The character
0 is written to indicate a zero value and
nothing is written to indicate a null string.
/usr/xpg6/bin/expr The
expr utility evaluates the expression and writes the result to
standard output followed by a NEWLINE. If there is no result from
expr processing, a NEWLINE is written to standard output.
OPERANDS
The
argument operand is evaluated as an expression. Terms of the
expression must be separated by blanks. Characters special to the shell
must be escaped (see
sh(1)). Strings containing blanks or other special
characters should be quoted. The length of the expression is limited to
LINE_MAX (2048 characters).
The operators and keywords are listed below. The list is in order of
increasing precedence, with equal precedence operators grouped within
{} symbols. All of the operators are left-associative.
expr \| expr Returns the evaluation of the first
expr if it is neither
NULL nor
0;
otherwise, returns the evaluation of the second
expr if it is not
NULL; otherwise,
0.
expr \& expr Returns the first
expr if neither
expr is
NULL or
0, otherwise
returns
0.
expr{
=,
\>,
\>=,
\<,
\<=,
!=}
expr Returns the result of an integer comparison if both arguments are
integers, otherwise returns the result of a string comparison using
the locale-specific coalition sequence. The result of each comparison
will be
1 if the specified relationship is
TRUE,
0 if the
relationship is
FALSE.
expr {
+,
- }
expr Addition or subtraction of integer-valued arguments.
expr {
\*,
/,
%}
expr Multiplication, division, or remainder of the integer-valued
arguments.
expr : expr The matching operator
: (colon) compares the first argument with the
second argument, which must be an internationalized basic regular
expression (BRE), except that all patterns are anchored to the
beginning of the string. That is, only sequences starting at the
first character of a string are matched by the regular expression.
See
regex(7) and NOTES. Normally, the
/usr/bin/expr matching operator
returns the number of bytes matched and the
/usr/xpg4/bin/expr matching operator returns the number of characters matched (
0 on
failure). If the second argument contains at least one BRE sub-
expression [\(...\)], the matching operator returns the string
corresponding to \1.
integer An argument consisting only of an (optional) unary minus followed by
digits.
string A string argument that cannot be identified as an
integer argument or
as one of the expression operator symbols.
Compatibility Operators (x86 only) The following operators are included for compatibility with INTERACTIVE
UNIX System only and are not intended to be used by non- INTERACTIVE UNIX
System scripts:
index string character-list Report the first position in which any one of the bytes in
character- list matches a byte in
string.
length string Return the length (that is, the number of bytes) of
string.
substr string integer-1 integer-2 Extract the substring of
string starting at position
integer-1 and of
length
integer-2 bytes. If
integer-1 has a value greater than the
number of bytes in
string,
expr returns a null string. If you try to
extract more bytes than there are in string,
expr returns all the
remaining bytes from
string. Results are unspecified if either
integer-1 or
integer-2 is a negative value.
EXAMPLES
Example 1: Adding an integer to a shell variable
Add 1 to the shell variable
a:
example$
a=`expr $a + 1` Example 2: Returning a path name segment
The following example emulates
basename(1), returning the last segment of
the path name
$a. For
$a equal to either
/usr/abc/file or just
file, the
example returns
file. (Watch out for
/ alone as an argument:
expr takes
it as the division operator. See NOTES below.)
example$
expr $a : '.*/\(.*\)' \| $a Example 3: Using // characters to simplify the expression
Here is a better version of the previous example. The addition of the
// characters eliminates any ambiguity about the division operator and
simplifies the whole expression.
example$
expr //$a : '.*/\(.*\)' /usr/bin/expr Example 4: Returning the number of bytes in a variable
example$
expr "$VAR" : '.*' /usr/xpg4/bin/expr Example 5: Returning the number of characters in a variable
example$
expr "$VAR" : '.*'ENVIRONMENT VARIABLES
See
environ(7) for descriptions of the following environment variables
that affect the execution of
expr:
LANG,
LC_ALL,
LC_COLLATE,
LC_CTYPE,
LC_MESSAGES, and
NLSPATH.
EXIT STATUS
As a side effect of expression evaluation,
expr returns the following
exit values:
0 If the expression is neither
NULL nor
0.
1 If the expression is either
NULL or
0.
2 For invalid expressions.
>2 An error occurred.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|CSI | enabled |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
SEE ALSO
basename(1),
ed(1),
sh(1),
Intro(3),
attributes(7),
environ(7),
regex(7),
standards(7)DIAGNOSTICS
syntax error Operator and operand errors.
non-numeric argument Arithmetic is attempted on such a string.
NOTES
After argument processing by the shell,
expr cannot tell the difference
between an operator and an operand except by the value. If
$a is an
=,
the command:
example$
expr $a = '=' looks like:
example$
expr = = = as the arguments are passed to
expr (and they are all taken as the
= operator). The following works:
example$
expr X$a = X= Regular Expressions
Unlike some previous versions,
expr uses Internationalized Basic Regular
Expressions for all system-provided locales. Internationalized Regular
Expressions are explained on the
regex(7) manual page.
August 29, 2003
EXPR(1)