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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.
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
expr | \ expr | Returns the ®rst expr if it is neither null nor 0, otherwise returns the second expr. | ||
expr | \& expr | Returns the ®rst expr if neither expr is null or 0, otherwise returns 0. | ||
expr { | =, | \>, | \>=, \<, \<=, != } expr | |
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| If both arguments are integers, and if the comparison is satis®ed, expr returns 1 other- |
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| wise it returns 0. expr returns the result of an integer comparison if both arguments |
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| are integers; otherwise returns the result of a lexical comparison (note that = and == |
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| are identical, in that both test for equality). |
expr { | +, | - } | expr | |
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| Addition or subtraction of decimal |
expr { | \∗, | /, % } expr | ||
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| Multiplication, division or remainder of decimal |
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| integer result. |
expr : expr The matching operator : compares the ®rst 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 Ã) and, therefore, Ã 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 ®rst argument.
length expr The length of expr.
substr expr expr expr
Takes the substring of the ®rst expr, starting at the character speci®ed by the second expr for the length given by the third expr.
index expr expr Returns the position in the ®rst expr which contains a character found in the second expr.
match | Match is a pre®x operator equivalent to the in®x operator :. |
\( ... \) | Grouping symbols. Any expression can be placed within parentheses. Parentheses can |
| be nested to a depth of EXPR_NEST_MAX as speci®ed in the header ®le |
| <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
LANG determines the language in which messages are displayed.
If LC_COLLATE or LC_CTYPE is not speci®ed in the environment or is set to the empty string, the value of LANG is used as a default for each unspeci®ed or empty variable. If LANG is not speci®ed or is set to the empty string, a default of "C" (see lang(5)) is used instead of LANG. If any internationalization variable contains an invalid setting, expr behaves as if all internationalization variables are set to "C" (see environ(5)).
Section 1−262 | − 1 − |