Chapter 23. Search and Replace Functions

[ expr =~ ] [ m ] /pattern/ [ g [ c ] ] [ i ] [ m ] [ o ] [ s ] [ x ]

Searches expr (default $_) for a pattern.

For =~, its negation !~ may be used, which is true when =~ would return false, and vice versa.

After a successful match, the following special variables are set:

$&

The string that matched.

$`

The string preceding what was matched.

$'

The string following what was matched.

$1

The first parenthesized subexpression that matched, $2 the second, and so on.

$+

The last subexpression that matched.

@-

The start offsets of the match and submatches.

@+

The corresponding end offsets.

If used in list context, a list is returned consisting of the subexpressions matched by the parentheses in pattern, i.e., ($1,$2,$3, . . . ).

Optional modifiers are:

c

(with g) prepares for continuation.

g

matches as many times as possible.

i

searches in a case-insensitive manner.

o

interpolates variables only once.

m

treats the string as multiple lines. ^ and $ will match at embedded newline characters.

s

treats the string as a single line. . will match embedded newline characters.

x

allows for whitespace and comments.

If pattern is empty, the most recent pattern from a previous successful m// or s/// is used.

With g, the match in scalar context can be used as an iterator. The iterator is reset upon failure, unless c is also supplied.

See generic Chapter 6.

?pattern?

This is just like the /pattern/ search, except that it matches only once between calls to the reset operator.

[ $var =~ ] s /pattern/newtext/ [ e ] [ g ] [ i ] [ m ] [ o ] [ s ] [ x ]

Searches the string var (default $_) for a pattern, and if found, replaces that part with the replacement text.

If successful, sets the special variables as described with m// and returns the number of substitutions made. Otherwise, it returns false.

Optional modifiers are:

g

replaces all occurrences of the pattern.

e

evaluates newtext as a Perl expression.

For the other modifiers, see m/pattern/ matching on the page before.

If pattern is empty, the most recent pattern from a previous successful m// or s/// is used.

See generic Chapter 6.

[ $var =~ ] tr/search/replacement/ [ c ] [ d ] [ s ]

Transliterates all occurrences of the characters found in the search list into the corresponding character in the replacement list. It returns the number of characters replaced.

Optional modifiers are:

c

complements the search list.

d

deletes all characters found in the search list that do not have a corresponding character in the replacement list.

s

squeezes all sequences of characters that are translated into the same target character into one occurrence of this character.

See generic Chapter 6.

[ $var =~ ] y/ search/replacement/modifiers

Identical to tr.

If the righthand side of the =~ or !~ is an expression rather than a search pattern, substitution, or transliteration, and its value is not the result of a qr operator, it is interpreted as a string and compiled into a search pattern at runtime.

pos scalar†

Returns the position where the last /g search in scalar left off. Alters the location of G if assigned to.

study scalar†

Studies the scalar in anticipation of performing many pattern matches on its contents before the variable is next modified.

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