NAME

expr − evaluate arguments as an expression

SYNOPSIS

/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 special to the shell must be escaped (see sh(1)).  Strings containing 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 operators 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 coalition 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 argument with the second argument, which must be an internationalized basic regular expression (BRE); see regex(5) and NOTES.  Normally, the /usr/bin/expr matching 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 (x86 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

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 out for / alone as an argument: expr takes it as the division operator; see NOTES below.) 

example$ expr $a : ´.∗/\(.∗\)´ \| $a

Here is a better version of the previous example.  The addition of the // characters eliminates any ambiguity about the division operator and simplifies the whole expression. 

example$ expr //$a : ´.∗/\(.∗\)´

/usr/bin/expr

Return the number of bytes in $VAR:

example$ expr "$VAR" : ´.∗´

/usr/xpg4/bin/expr

Return the number of characters in $VAR:

example$ expr "$VAR" : ´.∗´

ENVIRONMENT

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 attributes:

SEE ALSO

basename(1), ed(1), sh(1), Intro(3), attributes(5), environ(5), regex(5), xpg4(5)

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 5.6  —  Last change: 17 Mar 1997