expr(1) User Commands expr(1)NAMEexpr - 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 compari‐
son will be 1 if the specified relationship is TRUE, 0 if the rela‐
tionship is FALSE.
expr { +, − } expr
Addition or subtraction of integer-valued arguments.
expr { \*, /, %} expr
Multiplication, division, or remainder of the integer-valued argu‐
ments.
expr : expr
The matching operator : (colon) compares the first argument with
the second argument, which must be an internationalized basic regu‐
lar 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(5) and NOTES. Normally, the /usr/bin/expr matching opera‐
tor 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 cor‐
responding 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 charac‐
ter-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(5) 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(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWcsu │
├─────────────────────────────┼─────────────────────────────┤
│CSI │enabled │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSObasename(1), ed(1), sh(1), Intro(3), attributes(5), environ(5),
regex(5), standards(5)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 Regu‐
lar Expressions for all system-provided locales. Internationalized Reg‐
ular Expressions are explained on the regex(5) manual page.
SunOS 5.10 29 Aug 2003 expr(1)