expr
User Commands expr(1)NAME
expr - evaluate arguments as an expressionSYNOPSIS
/usr/bin/expr argument ... /usr/xpg4/bin/expr argument ...DESCRIPTION
The expr utility evaluates the expression and writes the result to standard output. The character 0 is written to indicate a zero value and nothing is written to indicate a null string.OPERANDS
The argument operand is evaluated as an expression. Terms of the expression must be separated by blanks. Characters spe- cial to the shell must be escaped (see sh(1)). Strings con- taining 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 opera- tors grouped within {} symbols. All of the operators are left-associative. 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 string comparison using the locale-specific coal- ition sequence. The result of each comparison will be 1 if the specified relationship is TRUE, 0 if the relationship is FALSE. 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 : (colon) compares the first SunOS 5.8 Last change: 17 Mar 1997 1 User Commands expr(1) argument with the second argument, which must be an internationalized basic regular expression (BRE); see regex(5) and NOTES. Normally, the /usr/bin/expr match- ing operator returns the number of bytes matched and the /usr/xpg4/bin/expr matching operator returns the number of characters matched (0 on failure). If the second argument contains at least one BRE sub- expression [\(...\)], the matching operator returns the string corresponding to \1. 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. Compatibility Operators (IA only) The following operators are included for compatibility with INTERACTIVE UNIX System only and are not intended to be used by non- INTERACTIVE UNIX System scripts: index string character-list Report the first position in which any one of the bytes in character-list matches a byte in string. length string Return the length (that is, the number of bytes) of string. substr string integer-1 integer-2 Extract the substring of string starting at position integer-1 and of length integer-2 bytes. If integer-1 has a value greater than the number of bytes in string, expr returns a null string. If you try to extract more bytes than there are in string, expr returns all the remaining bytes from string. Results are unspecified if either integer-1 or integer-2 is a negative value. EXAMPLES Example 1: Examples of the expr command. 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 $a equal to either /usr/abc/file or just file, the example returns file. (Watch SunOS 5.8 Last change: 17 Mar 1997 2 User Commands expr(1) out for / alone as an argument: expr takes it as the divi- sion operator; see NOTES below.) example$ expr $a : '.*/\(.*\)' \| $a Here is a better version of the previous example. The addi- tion of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression. example$ expr //$a : '.*/\(.*\)' /usr/bin/expr Example 2: Return the number of bytes in $VAR: example$ expr "$VAR" : '.*' /usr/xpg4/bin/expr Example 3: Return the number of characters in $VAR: example$ expr "$VAR" : '.*' ENVIRONMENT VARIABLES 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: 0 if the expression is neither NULL nor 0 1 if the expression is either NULL or 0 2 for invalid expressions. >2 an error occurred.ATTRIBUTES
See attributes(5) for descriptions of the following attri- butes: ____________________________________________________________ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | | Availability | SUNWcsu | | CSI | enabled | |_____________________________|_____________________________|SEE ALSO
basename(1), ed(1), sh(1), Intro(3), attributes(5), environ(5), regex(5), XPG4(5) SunOS 5.8 Last change: 17 Mar 1997 3 User Commands expr(1)DIAGNOSTICS
syntax error Operator and operand errors. non-numeric argument 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 Unlike some previous versions, expr uses Internationalized Basic Regular Expressions for all system-provided locales. Internationalized Regular Expressions are explained on the regex(5) manual page. SunOS 5.8 Last change: 17 Mar 1997 4