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)
