expr(1) General Commands Manual expr(1)
NAME
expr - Evaluates arguments as expressions
SYNOPSIS
expr expression
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
expr: XCU5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
OPTIONS
None
OPERANDS
The single expression evaluated by expr will be formed from the operands, as described in the DESCRIPTION section. Each of the expression
operator symbols: ( ) | & = > >= < <= != + - * / % : and the symbols integer and string in the DESCRIPTION sec-
tion must be provided as separate arguments to expr. Expression to be evaluated, formed as explained in the DESCRIPTION section.
DESCRIPTION
The expr command reads an expression, evaluates it, and writes the result to standard output. Within the expression argument, you must
separate each term with spaces, precede characters special to the shell with a (backslash), and quote strings containing spaces or other
special characters. Note that expr returns 0 to indicate a zero value, rather than the null string. Integers can be preceded by a unary
minus sign. Internally, integers are treated as 64-bit or 32-bit two's complement numbers, depending on the word size of the hardware
platform.
The operators and keywords are described in the following listing. Characters that need to be escaped are preceded by a (backslash).
The list is in order of increasing precedence with equal precedence operators grouped within {} (braces). Returns expression1 if it is
neither null nor 0 (zero); otherwise, returns expression2. Returns expression1 if neither expression1 nor expression2 is null nor 0; oth-
erwise, returns 0. Returns the result of an integer comparison if both expressions are integers; otherwise, returns the result of a string
comparison. Adds or subtracts integer-valued arguments. Multiplies, divides, or provides the remainder from the division of integer-val-
ued arguments. Compares expression1 with expression2, which must be a basic regular expression, with syntax as described for grep, except
that all patterns are anchored, so ^ (circumflex) (which anchors a pattern to the beginning of a line) is not a special character in this
context.
Normally, the matching operator returns the number of characters matched. Alternatively, you can use the (...) symbols in expres-
sion2 to return a portion of expression1. Provides expression grouping. An argument consisting only of an (optional) unary minus
followed by digits. A string argument. Refer to the STRING OPERAND section.
To avoid unpredictable results when using a range expression to match a class of characters, use a character class expression rather than a
standard range expression. For information about character class expressions, see the discussion of this topic included in the description
of the grep command.
FUNCTIONS
[Tru64 UNIX] The expr command provides the following string-expression functions. Strings containing white space must be quoted. A
string argument should not be one of the expression operator symbols shown in the OPERANDS section or one of the string function names
below. You cannot use, for example, match "$subject" "$pattern" unless it is confirmed that subject and pattern do not match this viola-
tion. The first character of a string is position 1. The information returned by all these functions is in the form of a string: [Tru64
UNIX] Compares each character in the second string against each character in the first string and returns the position in the first string
of the first match found, where the first match is the match closest to the beginning of string1. [Tru64 UNIX] Returns the length of the
string argument. [Tru64 UNIX] See the description of the : (colon) match operator, above. [Tru64 UNIX] Returns the substring of string
that begins at character position start and is length characters long.
STRING OPERAND
A string argument is an argument that cannot be identified as an integer argument or as one of the expression operator symbols shown in the
OPERANDS section.
The use of string arguments length, substr, index or match produces unspecified results.
EXIT STATUS
The expr command returns the following exit values: The expression is neither null nor 0. The expression is null or 0. The expression is
invalid. An error occurred.
EXAMPLES
To increment a shell variable, enter: COUNT=`expr $COUNT + 1`
This adds 1 to the COUNT shell variable (see sh for details). To find the length of a shell variable, enter: RES=`expr "$VAR" :
".*"`
Note that VAR is in double quotes to avoid problems where VAR is NULL or contains embedded spaces. The regular expression is also
quoted to avoid expansion by the shell. This operation can also be performed as: RES=`expr length "$VAR"` To use part of a shell
variable, enter: RES=`expr "$VAR" : "-*(.*)"`
This removes leading - (dashes), if any, from VAR. If the ( ) characters were omitted, RES would contain the length of VAR. To
find a character from one string in another string, enter: INDEX=`expr index "Hello World!" "Wo"`
Note that the returned value is 5, not 7. The first match is the fifth character in string1, matching the o in string2 rather than
the W, which is the seventh character in string1. Special considerations: RES=`expr "x$VAR" : "x-*(.*)"`
This succeeds even if VAR has the value - (dash). RES=`expr "x$VAR" = "x="
This succeeds even if VAR has the value = (equal sign).
ENVIRONMENT VARIABLES
The following environment variables affect the execution of expr: Provides a default value for the internationalization variables that are
unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari-
ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value,
overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as opposed to multibyte characters in arguments) and the behavior of character classes
in regular expressions.. Determines the locale for the format and contents of diagnostic messages written to standard error. Determines
the location of message catalogues for the processing of LC_MESSAGES.
SEE ALSO
Commands: grep(1), Bourne shell sh(1b), POSIX shell sh(1p), test(1)
Functions: string(3), wcscat(3)
Standards: standards(5)
expr(1)