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Name

expr - evaluate arguments as an expression

Synopsis

expr arguments

Availability

SUNWcsu

Description

The expr utility will evaluate the expression and write the result to standard output. The character 0 will be written to indicate a zero value and nothing will be written to indicate a NULL string.

Operands

arguments are taken as an expression. Terms of the expression must be separated by blanks. Characters special to the shell must be escaped (see sh(1) ). Strings containing blanks or other special characters should be quoted. The length of the expression is limited to LINE_MAX (2048 characters).

The operators and keywords are listed below. 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 or 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 (see NOTES). Normally, the matching operator returns the number of bytes matched (0 on failure).
( expr )
pattern symbols; can be used to return a portion of the first argument.
integer
An argument consisting only of an (optional) unary minus followed by digits.
string
A string argument that cannot be identified as an integer argument or as one of the expression operator symbols.

Examples

Add 1 to the shell variable a:

example$ 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 NOTES below.)

example$ 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.

example$ expr //$a : ’.*/\(.*\)’

Return the number of characters in $VAR :

example$ expr $VAR : ’.*’

Environment

See environ(5) for descriptions of the following environment variables that affect the execution of expr: LC_COLLATE , LC_CTYPE , LC_MESSAGES , and NLSPATH .

Exit Status

As a side effect of expression evaluation, expr returns the following exit values:
  1. if the expression is neither NULL nor 0
  2. if the expression is either NULL or 0
  3. for invalid expressions.
    >2
    an error occurred.

    Files

    /usr/lib/locale/locale/LC_COLLATE/CollTable
    collation table generated by localedef
    /usr/lib/locale/locale/LC_COLLATE/coll.so
    shared object containing string transformation library routines

    See Also

    basename(1) , ed(1) , sh(1) , environ(5) , regex(5) , regexp(5)

    Diagnostics

    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:

    example$ expr $a = ’=’

    looks like:

    example$ expr = = =

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

    example$ expr X$a = X=

    Regular Expressions

    Internationalized Regular Expressions are used in the POSIX and "C" locales. In other locales, Internationalized Regular Expressions are used if the following two conditions are met:

    • /usr/lib/locale/locale/LC_COLLATE /CollTable is present
    • /usr/lib/locale/locale/LC_COLLATE /coll.so is not present;

    otherwise, Simple Regular Expressions are used. Note that all patterns are ‘anchored’ (that is, begin with ^) and, therefore, ^ is not a special character in that context.

    Internationalized Regular Expressions are explained on regex(5) .
    Simple Regular Expressions are explained on regexp(5) .

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