NAME

expr − evaluate arguments as an expression

SYNOPSIS

expr arguments

DESCRIPTION

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, 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.

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 (note that = and == are identical, in that both test for equality).

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.  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 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.

indexexpr 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 (value given in 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 characters 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 variable contains an invalid setting, expr behaves as if all internationalization variables are set to "C" (see environ(5)).

International Code Set Support

Single- and multi-byte character code sets are supported. 

EXAMPLES

a=‘expr $a + 1‘
Adds 1 to the shell variable a. 

expr $a :  ’.∗/\(.∗\)’  \|  $a
For $a equal to either "/usr/abc/file" or just "file", this example returns the last segment of a path name (i.e., file).  Watch out for / alone as an argument because expr interprets it as the division operator (see WARNINGS below). 

expr //$a :  ’.∗/\(.∗\)’
This is a better representation of the previous example. The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression. 

expr $VAR  :  ’.∗’
Returns the number of characters in $VAR. 

RETURN VALUE

As a side effect of expression evaluation, expr returns the following exit values:

0 Expression is neither null nor 0

1 Expression is null or 0

2 Invalid expression. 

>2 An error occurred while evaluating the expression. 

SEE ALSO

sh(1), test(1), environ(5), lang(5), regexp(5). 

DIAGNOSTICS

syntax error Operator or operand errors

non-numeric argument Arithmetic attempted on a string

WARNINGS

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  =  ’=’

resembles:

expr  =  =  =

as the arguments are passed to expr (and they will all be taken as the = operator).  The following works:

expr X$a = X=

STANDARDS CONFORMANCE

expr: SVID2, XPG2, XPG3, proposed POSIX.2 FIPS (June 1990)

Hewlett-Packard Company  —  HP-UX Release 8.05: June 1991