expr - Evaluates arguments as expressions
expr expression
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.
None
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 section must
be provided as separate arguments to expr. Expression to
be evaluated, formed as explained in the DESCRIPTION section.
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; otherwise, 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-valued 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 expression2 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 [Toc] [Back]
[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 violation. 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 [Toc] [Back]
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.
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.
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). When CMD_ENV variable is set to bsd:
RES=`expr 0001'
This results in 0001. Otherwise the value is 1.
RES=`expr substr 012345 1 3'
This results in 012. Otherwise the value is 12.
ENVIRONMENT VARIABLES [Toc] [Back] The following environment variables affect the execution
of expr: [Tru64 UNIX] This variable, if set to bsd, prevents
stripping of leading zeroes from expressions. 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 variables 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.
Commands: grep(1), Bourne shell sh(1b), POSIX shell
sh(1p), test(1)
Functions: string(3), wcscat(3)
Standards: standards(5)
expr(1)
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