# expr

Evaluate expressions, evaluates an expression and writes the result on standard output. A blank line below separates increasing precedence groups.

Syntax

expr expression expr option

Options

--help Display help and exit --version output version information and exit

Expressions

ARG1 | ARG2 ARG1 if it is neither null nor 0, otherwise ARG2 ARG1 & ARG2 ARG1 if neither argument is null or 0, otherwise 0 ARG1 < ARG2 ARG1 is less than ARG2 ARG1 <= ARG2 ARG1 is less than or equal to ARG2 ARG1 = ARG2 ARG1 is equal to ARG2 ARG1 != ARG2 ARG1 is unequal to ARG2 ARG1 >= ARG2 ARG1 is greater than or equal to ARG2 ARG1 > ARG2 ARG1 is greater than ARG2 ARG1 + ARG2 Arithmetic sum of ARG1 and ARG2 ARG1 - ARG2 Arithmetic difference of ARG1 and ARG2 ARG1 * ARG2 Arithmetic product of ARG1 and ARG2 ARG1 / ARG2 Arithmetic quotient of ARG1 divided by ARG2 ARG1 % ARG2 Arithmetic remainder of ARG1 divided by ARG2 STRING : REGEXP Anchored pattern match of REGEXP in STRING match STRING REGEXP Same as STRING : REGEXP substr STRING POS LENGTH Substring of STRING, POS counted from 1 index STRING CHARS Index in STRING where any CHARS is found, or 0 length STRING Length of STRING + TOKEN Interpret TOKEN as a string, even if it is a keyword like 'match' or an operator like '/' ( EXPRESSION ) Value of EXPRESSION

Beware that many operators need to be escaped or quoted for shells.

Comparisons are arithmetic if both ARGs are numbers, else lexicographical.

Pattern matches return the string matched between \( and \) or null;

if \( and \) are not used, they return the number of characters matched or 0.

Exit status

0 if EXPRESSION is neither null nor 0,

1 if EXPRESSION is null or 0,

2 if EXPRESSION is syntactically invalid,

3 if an error occurred.

Each token of the expression must be a separate argument.

Operands are either numbers or strings. `expr’ coerces anything appearing in an operand position to an integer or a string depending on the operation being applied to it.

Strings are not quoted for `expr’ itself, though you might need to quote them to protect characters with special meaning to the shell, e.g., spaces.

Operators can be given as infix symbols or prefix keywords. Parentheses may be used for grouping in the usual manner (you must quote parentheses to avoid the shell evaluating them, however).

String expressions

`expr’ supports pattern matching and other string operators. These have lower precedence than both the numeric and relational operators (in the next sections).

STRING : REGEX

Perform pattern matching. The arguments are coerced to strings and the second is considered to be a (basic, a la GNU `grep') regular expression, with a `^' implicitly prepended. The first argument is then matched against this regular expression. If the match succeeds and REGEX uses `\(' and `\)', the `:' expression returns the part of STRING that matched the subexpression; otherwise, it returns the number of characters matched. If the match fails, the `:' operator returns the null string if `\(' and `\)' are used in REGEX, otherwise 0. Only the first `\( ... \)' pair is relevant to the return value; additional pairs are meaningful only for grouping the regular expression operators. In the regular expression, `\+', `\?', and `\|' are operators which respectively match one or more, zero or one, or separate alternatives. SunOS and other `expr''s treat these as regular characters. (POSIX allows either behavior.) match STRING REGEX An alternative way to do pattern matching. This is the same as STRING : REGEX. substr STRING POSITION LENGTH Returns the substring of STRING beginning at POSITION with length at most LENGTH. If either POSITION or LENGTH is negative, zero, or non-numeric, returns the null string. index STRING CHARSET Returns the first position in STRING where the first character in CHARSET was found. If no character in CHARSET is found in STRING, return 0. length STRING Returns the length of STRING. quote TOKEN Interpret TOKEN as a string, even if it is a keyword like MATCH or an operator like /. This makes it possible to test `expr length quote "$x"' or `expr quote "$x" : '.*/\(.\)'' and have it do the right thing even if the value of $X happens to be (for example) `/' or `index'. This operator is a GNU extension. It is disabled when the environment variable `POSIXLY_CORRECT' is set.

To make `expr’ interpret keywords as strings, you must use the

`quote’ operator.

Numeric expressions

`expr’ supports the usual numeric operators, in order of increasing precedence. The string operators (previous section) have lower precedence, the connectives (next section) have higher.

+ –

Addition and subtraction. Both arguments are coerced to numbers;

an error occurs if this cannot be done.

* / %

Multiplication, division, remainder. Both arguments are coerced to

numbers; an error occurs if this cannot be done.

Relations for `expr’

`expr’ supports the usual logical connectives and relations. These are higher precedence than either the string or numeric operators (previous sections). Here is the list, lowest-precedence operator first.

| Returns its first argument if that is neither null nor 0,

otherwise its second argument.

& Return its first argument if neither argument is null or 0,

otherwise 0.

< <= = == != >= >

Compare the arguments and return 1 if the relation is true, 0

otherwise. `==’ is a synonym for `=’. `expr’ first tries to

coerce both arguments to numbers and do a numeric comparison; if

either coercion fails, it does a lexicographic comparison.

Examples

# A partial match will return the number of characters that match:

$ expr ss64 : ss6

3

# The condition in string 2 must entirely match string 1

$ expr ss64 : ss7

0

# Adding numbers

$ expr 5 + 2

7

# When multiplying the * has to be escaped

$ expr 5 \* 3

15

# Incrementing a variable (arithmetic expansion)

$ demo=1

$ demo=`expr $demo + 1`

$ echo $demo

2

$ demo=`expr $demo + 1`

$ echo $demo

3

# To print the non-directory part of the file name stored in `$fname’,

which need not contain a `/’.

$ expr $fname : ‘.*/\(^.*\)’ ‘^|’ $fname

$ expr abc : ‘a\(.\)c’

b

$ expr index abcdef cz

3

$ expr index index a

expr: syntax error

$ expr index quote index a

0