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+expr(P) expr(P)
+
+
+
+
+
+NAME
+ expr - evaluate arguments as an expression
+
+SYNOPSIS
+ expr operand
+
+DESCRIPTION
+ The expr utility shall evaluate an expression and write
+ the result to standard output.
+
+OPTIONS
+ None.
+
+OPERANDS
+ The single expression evaluated by expr shall be formed
+ from the operands, as described in the EXTENDED DESCRIP-
+ TION section. The application shall ensure that each of
+ the expression operator symbols:
+
+
+ ( ) | & = > >= < <= != + - * / % :
+
+ and the symbols integer and string in the table are pro-
+ vided as separate arguments to expr.
+
+STDIN
+ Not used.
+
+INPUT FILES
+ None.
+
+ENVIRONMENT VARIABLES
+ The following environment variables shall affect the
+ execution of expr:
+
+ LANG Provide a default value for the internationaliza-
+ tion variables that are unset or null. (See the
+ Base Definitions volume of IEEE Std 1003.1-2001,
+ Section 8.2, Internationalization Variables for
+ the precedence of internationalization variables
+ used to determine the values of locale cate-
+ gories.)
+
+ LC_ALL If set to a non-empty string value, override the
+ values of all the other internationalization
+ variables.
+
+ LC_COLLATE
+
+ Determine the locale for the behavior of ranges,
+ equivalence classes, and multi-character collat-
+ ing elements within regular expressions and by
+ the string comparison operators.
+
+ LC_CTYPE
+ Determine the locale for the interpretation of
+ sequences of bytes of text data as characters
+ (for example, single-byte as opposed to multi-
+ byte characters in arguments) and the behavior of
+ character classes within regular expressions.
+
+ LC_MESSAGES
+ Determine the locale that should be used to
+ affect the format and contents of diagnostic
+ messages written to standard error.
+
+ NLSPATH
+ Determine the location of message catalogs for
+ the processing of LC_MESSAGES .
+
+
+ASYNCHRONOUS EVENTS
+ Default.
+
+STDOUT
+ The expr utility shall evaluate the expression and write
+ the result, followed by a <newline>, to standard output.
+
+STDERR
+ The standard error shall be used only for diagnostic
+ messages.
+
+OUTPUT FILES
+ None.
+
+EXTENDED DESCRIPTION
+ The formation of the expression to be evaluated is shown
+ in the following table. The symbols expr, expr1, and
+ expr2 represent expressions formed from integer and
+ string symbols and the expression operator symbols (all
+ separate arguments) by recursive application of the con-
+ structs described in the table. The expressions are
+ listed in order of increasing precedence, with equal-
+ precedence operators grouped between horizontal lines.
+ All of the operators shall be left-associative.
+Expression Description
+expr1 | expr2 Returns the evaluation of expr1 if it is neither null nor zero; otherwise, returns the evaluation of expr2 if it is not null; otherwise, zero.
+expr1 & expr2 Returns the evaluation of expr1 if neither expression evaluates to null or zero; otherwise, returns zero.
+ Returns the result of a decimal integer comparison if both arguments are integers; otherwise, returns the result of a string comparison using the locale-specific collation sequence. The result of each comparison is 1 if the specified relationship is true, or 0 if the relationship is false.
+expr1 = expr2 Equal.
+expr1 > expr2 Greater than.
+expr1 >= expr2 Greater than or equal.
+expr1 < expr2 Less than.
+expr1 <= expr2 Less than or equal.
+expr1 != expr2 Not equal.
+expr1 + expr2 Addition of decimal integer-valued arguments.
+expr1 - expr2 Subtraction of decimal integer-valued arguments.
+expr1 * expr2 Multiplication of decimal integer-valued arguments.
+expr1 / expr2 Integer division of decimal integer-valued arguments, producing an integer result.
+expr1 % expr2 Remainder of integer division of decimal integer-valued arguments.
+expr1 : expr2 Matching expression; see below.
+( expr ) Grouping symbols. Any expression can be placed within parentheses. Parentheses can be nested to a depth of {EXPR_NEST_MAX}.
+integer An argument consisting only of an (optional) unary minus followed by digits.
+string A string argument; see below.
+
+ Matching Expression
+ The ':' matching operator shall compare the string
+ resulting from the evaluation of expr1 with the regular
+ expression pattern resulting from the evaluation of
+ expr2. Regular expression syntax shall be that defined
+ in the Base Definitions volume of IEEE Std 1003.1-2001,
+ Section 9.3, Basic Regular Expressions, except that all
+ patterns are anchored to the beginning of the string
+ (that is, only sequences starting at the first character
+ of a string are matched by the regular expression) and,
+ therefore, it is unspecified whether '^' is a special
+ character in that context. Usually, the matching opera-
+ tor shall return a string representing the number of
+ characters matched ( '0' on failure). Alternatively, if
+ the pattern contains at least one regular expression
+ subexpression "[\(...\)]" , the string corresponding to
+ "\1" shall be returned.
+
+ String Operand
+ A string argument is an argument that cannot be identi-
+ fied 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 following exit values shall be returned:
+
+ 0 The expression evaluates to neither null nor
+ zero.
+
+ 1 The expression evaluates to null or zero.
+
+ 2 Invalid expression.
+
+ >2 An error occurred.
+
+
+CONSEQUENCES OF ERRORS
+ Default.
+
+ The following sections are informative.
+
+APPLICATION USAGE
+ After argument processing by the shell, expr is not
+ required to be able to tell the difference between an
+ operator and an operand except by the value. If "$a" is
+ '=' , the command:
+
+
+ expr $a = '='
+
+ looks like:
+
+
+ expr = = =
+
+ as the arguments are passed to expr (and they all may be
+ taken as the '=' operator). The following works reli-
+ ably:
+
+
+ expr X$a = X=
+
+ Also note that this volume of IEEE Std 1003.1-2001 per-
+ mits implementations to extend utilities. The expr util-
+ ity permits the integer arguments to be preceded with a
+ unary minus. This means that an integer argument could
+ look like an option. Therefore, the conforming applica-
+ tion must employ the "--" construct of Guideline 10 of
+ the Base Definitions volume of IEEE Std 1003.1-2001,
+ Section 12.2, Utility Syntax Guidelines to protect its
+ operands if there is any chance the first operand might
+ be a negative integer (or any string with a leading
+ minus).
+
+EXAMPLES
+ The expr utility has a rather difficult syntax:
+
+ Many of the operators are also shell control
+ operators or reserved words, so they have to be
+ escaped on the command line.
+
+ Each part of the expression is composed of sepa-
+ rate arguments, so liberal usage of <blank>s is
+ required. For example:
+ Invalid Valid
+
+ expr 1+2 expr 1 + 2
+ expr "1 + 2" expr 1 + 2
+ expr 1 + (2 * 3) expr 1 + \( 2 \* 3 \)
+
+ In many cases, the arithmetic and string features pro-
+ vided as part of the shell command language are easier
+ to use than their equivalents in expr. Newly written
+ scripts should avoid expr in favor of the new features
+ within the shell; see Parameters and Variables and
+ Arithmetic Expansion .
+
+ The following command:
+
+
+ a=$(expr $a + 1)
+
+ adds 1 to the variable a.
+
+ The following command, for "$a" equal to either
+ /usr/abc/file or just file:
+
+
+ expr $a : '.*/\(.*\)' \| $a
+
+ returns the last segment of a pathname (that is, file).
+ Applications should avoid the character '/' used alone
+ as an argument; expr may interpret it as the division
+ operator.
+
+ The following command:
+
+
+ expr "//$a" : '.*/\(.*\)'
+
+ 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. Also note that pathnames may contain charac-
+ ters contained in the IFS variable and should be quoted
+ to avoid having "$a" expand into multiple arguments.
+
+ The following command:
+
+
+ expr "$VAR" : '.*'
+
+ returns the number of characters in VAR.
+
+RATIONALE
+ In an early proposal, EREs were used in the matching
+ expression syntax. This was changed to BREs to avoid
+ breaking historical applications.
+
+ The use of a leading circumflex in the BRE is unspeci-
+ fied because many historical implementations have
+ treated it as a special character, despite their system
+ documentation. For example:
+
+
+ expr foo : ^foo expr ^foo : ^foo
+
+ return 3 and 0, respectively, on those systems; their
+ documentation would imply the reverse. Thus, the anchor-
+ ing condition is left unspecified to avoid breaking his-
+ torical scripts relying on this undocumented feature.
+
+FUTURE DIRECTIONS
+ None.
+
+SEE ALSO
+ Parameters and Variables , Arithmetic Expansion
+
+COPYRIGHT
+ Portions of this text are reprinted and reproduced in
+ electronic form from IEEE Std 1003.1, 2003 Edition,
+ Standard for Information Technology -- Portable Operat-
+ ing System Interface (POSIX), The Open Group Base Speci-
+ fications Issue 6, Copyright (C) 2001-2003 by the Insti-
+ tute of Electrical and Electronics Engineers, Inc and
+ The Open Group. In the event of any discrepancy between
+ this version and the original IEEE and The Open Group
+ Standard, the original IEEE and The Open Group Standard
+ is the referee document. The original Standard can be
+ obtained online at http://www.open-
+ group.org/unix/online.html .
+
+
+
+POSIX 2003 expr(P)