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Perl Format String Syntax

Perl-style format strings treat all characters as literals except '$' and '\' which start placeholder and escape sequences respectively.

Placeholder sequences specify that some part of what matched the regular expression should be sent to output as follows:

Placeholder

Meaning

$&

Outputs what matched the whole expression.

$MATCH

As $&

${^MATCH}

As $&

$`

Outputs the text between the end of the last match found (or the start of the text if no previous match was found), and the start of the current match.

$PREMATCH

As $`

${^PREMATCH}

As $`

$'

Outputs all the text following the end of the current match.

$POSTMATCH

As $'

${^POSTMATCH}

As $'

$+

Outputs what matched the last marked sub-expression in the regular expression.

$LAST_PAREN_MATCH

As $+

$LAST_SUBMATCH_RESULT

Outputs what matched the last sub-expression to be actually matched.

$^N

As $LAST_SUBMATCH_RESULT

$$

Outputs a literal '$'

$n

Outputs what matched the n'th sub-expression.

${n}

Outputs what matched the n'th sub-expression.

$+{NAME}

Outputs whatever matched the sub-expression named "NAME".

Any $-placeholder sequence not listed above, results in '$' being treated as a literal.

An escape character followed by any character x, outputs that character unless x is one of the escape sequences shown below.

Escape

Meaning

\a

Outputs the bell character: '\a'.

\e

Outputs the ANSI escape character (code point 27).

\f

Outputs a form feed character: '\f'

\n

Outputs a newline character: '\n'.

\r

Outputs a carriage return character: '\r'.

\t

Outputs a tab character: '\t'.

\v

Outputs a vertical tab character: '\v'.

\xDD

Outputs the character whose hexadecimal code point is 0xDD

\x{DDDD}

Outputs the character whose hexadecimal code point is 0xDDDDD

\cX

Outputs the ANSI escape sequence "escape-X".

\D

If D is a decimal digit in the range 1-9, then outputs the text that matched sub-expression D.

\l

Causes the next character to be outputted, to be output in lower case.

\u

Causes the next character to be outputted, to be output in upper case.

\L

Causes all subsequent characters to be output in lower case, until a \E is found.

\U

Causes all subsequent characters to be output in upper case, until a \E is found.

\E

Terminates a \L or \U sequence.


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