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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
expression
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).
expression1 \| expression2
Returns expression1 if it is neither null nor 0 (zero); otherwise,
returns expression2.
expression1 \!> expression2
Returns expression1 if neither expression1 nor expression2 is null nor
0; otherwise, returns 0.
expression1 { =, \>, \>=, \<, \<=, != } expression2
Returns the result of an integer comparison if both expressions are
integers; otherwise, returns the result of a string comparison.
expression1 {+, - } expression2
Adds or subtracts integer-valued arguments.
expression1 { \*, /, % } expression2
Multiplies, divides, or provides the remainder from the division of
integer-valued arguments.
expression1 : expression2 or match expression1 expression2
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.
(expression)
Provides expression grouping.
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. The first
character of a string is position 1. The information returned by all of
these functions is in the form of a string:
index string1 string2
[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.
length string
[Tru64 UNIX] Returns the length of the string argument.
match string1 string2
[Tru64 UNIX] See the description of the : (colon) match operator,
above.
substr string start length
[Tru64 UNIX] Returns the substring of string that begins at character
position start and is length characters long.
EXIT STATUS
The expr command returns the following exit values:
0 The expression is neither null nor 0.
1 The expression is null or 0.
2 The expression is invalid.
>2 An error occurred.
EXAMPLES
1. To increment a shell variable, enter:
COUNT=`expr $COUNT + 1`
This adds 1 to the COUNT shell variable (see sh for details).
2. To find the length of a shell variable, enter:
RES=`expr "$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 "$VAR"`
3. To use part of a shell variable, enter:
RES=`expr "$VAR" : "-*\(.*\)"`
This removes leading - (dashes), if any, from VAR. If the \( \)
characters were omitted, RES would contain the length of VAR.
4. 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.
5. 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:
LANG
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.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
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..
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
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)
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