expr.1 (2010 09)

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expr(1) expr(1)
NAME
expr - evaluate arguments as an expression
SYNOPSIS
expr arguments
DESCRIPTION
expr 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 0, 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. Internally, 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 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 .
In the UNIX 2003 environment,
expr returns 0 if the first expr is null or
0 and the
second expr is null.
expr
\& expr Returns the first expr if neither expr is null or
0, otherwise returns 0.
expr
{ =, \>, \>=, \<, \<=, != } expr
If both arguments are integers, and if the comparison is satisfied, expr returns 1
oth-
erwise it returns
0. expr returns the result of an integer comparison if both argu-
ments are integers; otherwise returns the result of a lexical comparison (note that =
and == are identical, in that both test for equality).
expr
{ +, - } expr
Addition or subtraction of decimal integer-valued arguments.
expr {
\*, /, % } expr
Multiplication, division or remainder of decimal integer-valued arguments producing
an integer result.
expr
: expr The matching operator : compares the first argument with the second argument
which must be a regular expression. expr supports the Basic Regular Expression syn-
tax (see regexp(5)), except that all patterns are ‘‘anchored’’ (i.e., begin with ˆ) and,
therefore, ˆ is not a special character, in that context. Normally, the matching
operator returns the number of characters matched (0 on failure). Alternatively, the
\( ... \) pattern symbols can be used to return a portion of the first argument.
length expr The length of expr.
substr expr expr expr
Takes the substring of the first expr , starting at the character specified by the second
expr for the length given by the third expr.
index expr expr Returns the position in the first expr which contains a character found in the second
expr .
match 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 EXPR_NEST_MAX as specified in the header file
<limits.h>.
EXTERNAL INFLUENCES
Environment Variables
LC_COLLATE determines the collating sequence used in evaluating regular expressions and the behavior
of the relational operators when comparing string values.
LC_CTYPE determines the interpretation of text as single- and/or multi-byte characters, and the charac-
ters matched by character class expressions in regular expressions.
LANG determines the language in which messages are displayed.
If
LC_COLLATE or LC_CTYPE is not specified in the environment or is set to the empty string, the value
of LANG is used as a default for each unspecified or empty variable. If LANG is not specified or is set to
the empty string, a default of "C" (see lang(5)) is used instead of LANG. If any internationalization
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