expr(1)expr(1)NAMEexpr - evaluate arguments as an expression
takes arguments as an expression, evaluates, then writes the result on
the standard output. Terms in the expression must be separated by
blanks. Characters special to the shell must be escaped. Note that
rather than the null string, is returned to indicate a zero value.
Strings containing blanks or other special characters should be quoted.
Integer-valued arguments can be preceded by a unary minus sign. Inter‐
nally, integers are treated as 32-bit, 2's complement numbers.
The operators and keywords are listed below. Characters that need to
be escaped are preceded by The list is in order of increasing prece‐
dence with equal-precedence operators grouped within symbols.
Returns the first expr if it is neither null nor otherwise returns the
In the UNIX 2003 environment, returns 0 if the first
expr is null or and the second expr is null.
Returns the first expr if neither expr is null or otherwise returns
If both arguments are integers, and if the comparison is satisfied,
expr returns otherwise it returns expr returns the
result of an integer comparison if both arguments are
integers; otherwise returns the result of a lexical
comparison (note that and are identical, in that both
test for equality).
Addition or subtraction of decimal integer-valued arguments.
Multiplication, division or remainder of decimal
integer-valued arguments producing an integer result.
The matching operator
compares the first argument with the second argument
which must be a regular expression. expr supports
the Basic Regular Expression syntax (see regexp(5)),
except that all patterns are ``anchored'' (i.e.,
begin with and, therefore, is not a special charac‐
ter, in that context. Normally, the matching opera‐
tor returns the number of characters matched (0 on
failure). Alternatively, the pattern symbols can be
used to return a portion of the first argument.
The length of expr.
Takes the substring of the first
expr, starting at the character specified by the sec‐
ond expr for the length given by the third expr.
Returns the position in the first
expr which contains a character found in the second
Match is a prefix operator equivalent to the infix operator
Grouping symbols. Any expression can be placed within parentheses.
Parentheses can be nested to a depth of as specified
in the header file
determines the collating sequence used in evaluating regular expres‐
sions and the behavior of the relational operators when comparing
determines the interpretation of text as single- and/or multi-byte
characters, and the characters matched by character class expressions
in regular expressions.
determines the language in which messages are displayed.
If or is not specified in the environment or is set to the empty
string, the value of is used as a default for each unspecified or empty
variable. If is not specified or is set to the empty string, a default
of "C" (see lang(5)) is used instead of If any internationalization
variable contains an invalid setting, behaves as if all international‐
ization variables are set to "C" (see environ(5)).
If is set to it enables the UNIX 2003 Standard environment.
International Code Set Support
Single- and multi-byte character code sets are supported.
As a side effect of expression evaluation, expr returns the following
Expression is neither null nor zero.
Expression is null or zero.
An error occurred while evaluating the expression.
Operator or operand errors
Arithmetic attempted on a string
Add 1 to the shell variable
For equal to either or just return the last segment of a path name
(i.e., Beware of alone as an argument because expr interprets it as the
division operator (see below):
A better representation of the previous example. The addition of the
characters eliminates any ambiguity about the division operator and
simplifies the whole expression:
Return the number of characters in
After argument processing by the shell, expr cannot tell the difference
between an operator and an operand except by the value. If is an the
as the arguments are passed to expr (and they will all be taken as the
operator). The following works:
was developed by OSF and HP.
SEE ALSOsh(1), test(1), environ(5), lang(5), regexp(5).