expr(1B) SunOS/BSD Compatibility Package Commands expr(1B)NAMEexpr - evaluate arguments as a logical, arithmetic, or string expres‐
sion
SYNOPSIS
/usr/ucb/expr argument...
DESCRIPTION
The expr utility evaluates expressions as specified by its arguments.
After evaluation, the result is written on the standard output. Each
token of the expression is a separate argument, so terms of the expres‐
sion must be separated by blanks. Characters special to the shell must
be escaped. Note: 0 is returned to indicate a zero value, rather than
the null string. Strings containing blanks or other special characters
should be quoted. Integer-valued arguments may be preceded by a unary
minus sign. Internally, integers are treated as 32-bit, two's-comple‐
ment numbers.
The operators and keywords are listed below. Characters that need to be
escaped are preceded by `\'. The list is in order of increasing prece‐
dence, with equal precedence operators grouped within {} symbols.
expr \| expr
Returns the evaluation of the first expr if it is neither NULL nor
0; otherwise, returns the evaluation of the second expr if it is
not NULL; otherwise, 0.
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 lexical comparison.
expr { +, − } expr
Addition or subtraction of integer-valued arguments.
expr { \, /, % } expr
Multiplication, division, or remainder of the integer-valued argu‐
ments.
string : regular-expression
match string regular-expression
The two forms of the matching operator above are synonymous. The
matching operators : and match compare the first argument with the
second argument which must be a regular expression. Regular expres‐
sion syntax is the same as that of regexp(5), except that all pat‐
terns are "anchored" (treated as if they begin with ^) and there‐
fore ^ is not a special character, in that context. Normally, the
matching operator returns the number of characters matched (0 on
failure). Alternatively, the \...\ pattern symbols can be used to
return a portion of the first argument.
substr string integer-1 integer-2
Extracts the substring of string starting at position integer-1
and of length integer-2 characters. If integer-1 has a value
greater than the length of string, expr returns a null string. If
you try to extract more characters than there are in string, expr
returns all the remaining characters from string. Beware of using
negative values for either integer-1 or integer-2 as expr tends to
run forever in these cases.
index string character-list
Reports the first position in string at which any one of the char‐
acters in character-list matches a character in string.
length string
Returns the length (that is, the number of characters) of string.
( expr )
Parentheses may be used for grouping.
EXAMPLES
Example 1 Adding an integer to a shell variable
Add 1 to the shell variable a.
a='expr $a + 1'
Example 2 Returning a path name segment
Return the last segment of a path name (that is, the filename part).
Watch out for / alone as an argument: expr will take it as the division
operator (see BUGS below).
# 'For $a equal to either "/usr/abc/file" or just "file"'
expr $a : '.*/\ \ $a
Example 3 Using // characters to simplify the expression
The addition of the // characters eliminates any ambiguity about the
division operator and simplifies the whole expression.
# A better representation of example 2.
expr //$a : '.*/\
Example 4 Returning the value of a variable
Returns the number of characters in $VAR.
expr $VAR : '.*'
EXIT STATUSexpr returns the following exit codes:
0 If the expression is neither NULL nor 0.
1 If the expression is NULL or 0.
2 For invalid expressions.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │compatibility/ucb │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOsh(1), test(1), attributes(5), regexp(5)DIAGNOSTICS
syntax error for operator/operand errors
non-numeric argument if arithmetic is attempted on such a string
division by zero if an attempt to divide by zero is made
BUGS
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:
expr $a = '='
looks like:
expr = = =
as the arguments are passed to expr (and they will all be taken as the
= operator). The following works:
expr X$a = X=
Note: the match, substr, length, and index operators cannot themselves
be used as ordinary strings. That is, the expression:
example% expr index expurgatorious length
syntax error
example%
generates the `syntax error' message as shown instead of the value 1 as
you might expect.
SunOS 5.11 6 Jun 2000 expr(1B)