expr(1)
NAME
expr − evaluate arguments as an expression
SYNOPSIS
expr arguments
AVAILABILITY
SUNWcsu
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.
USAGE
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
returns the first expr if it is neither null nor 0, otherwise returns the second expr.
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 lexical comparison.
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 : compares 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 bytes matched (0 on failure). Alternatively, the \(...\) pattern symbols can be used to return a portion of the first argument.
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. (Watch out for / alone as an argument: expr takes it as the division operator; see the NOTES below.)
expr $a : ´.∗/\(.∗\)´ \| $a
Here is a better version of the previous example. The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression.
expr //$a : ´.∗/\(.∗\)´
Return the number of characters in $VAR:
expr $VAR : ´.∗´
ENVIRONMENT
If any of the LC_∗ variables ( LC_CTYPE, LC_MESSAGES, LC_TIME, LC_COLLATE, LC_NUMERIC, and LC_MONETARY ) (see environ(5)) are not set in the environment, the operational behavior of expr for each corresponding locale category is determined by the value of the LANG environment variable. If LC_ALL is set, its contents are used to override both the LANG and the other LC_∗ variables. If none of the above variables is set in the environment, the "C" (U.S. style) locale determines how expr behaves.
LC_CTYPE
Determines how expr handles characters. When LC_CTYPE is set to a valid value, expr can display and handle text and filenames containing valid characters for that locale. expr can display and handle Extended Unix Code (EUC) characters where any individual character can be 1, 2, or 3 bytes wide. expr can also handle EUC characters of 1, 2, or more column widths. In the "C" locale, only characters from ISO 8859-1 are valid.
LC_MESSAGES
Determines how diagnostic and informative messages are presented. This includes the language and style of the messages, and the correct form of affirmative and negative responses. In the "C" locale, the messages are presented in the default form found in the program itself (in most cases, U.S. English).
SEE ALSO
DIAGNOSTICS
As a side effect of expression evaluation, expr returns the following exit values:
0if the expression is neither null nor 0
1if the expression is null or 0
2for invalid expressions.
syntax error for operator/operand errors
non-numeric argument
if 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:
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=
SunOS 5.4 — Last change: 14 Sep 1992