Escape Sequences (The GNU Awk User’s Guide)
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3.2 Escape Sequences
Some characters cannot be included literally in string constants ("foo"
) or regexp constants (/foo/
). Instead, they should be represented with escape sequences, which are character sequences beginning with a backslash (‘\
’). One use of an escape sequence is to include a double-quote character in a string constant. Because a plain double quote ends the string, you must use ‘\"
’ to represent an actual double-quote character as a part of the string. For example:
$ awk 'BEGIN { print "He said \"hi!\" to her." }' -| He said "hi!" to her.
The backslash character itself is another character that cannot be included normally; you must write ‘\\
’ to put one backslash in the string or regexp. Thus, the string whose contents are the two characters ‘"
’ and ‘\
’ must be written "\"\\"
.
Other escape sequences represent unprintable characters such as TAB or newline. There is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, but they may look ugly.
The following list presents all the escape sequences used in awk
and what they represent. Unless noted otherwise, all these escape sequences apply to both string constants and regexp constants:
\\
A literal backslash, ‘
\
’.\a
The “alert” character, Ctrl-g, ASCII code 7 (BEL). (This often makes some sort of audible noise.)
\b
Backspace, Ctrl-h, ASCII code 8 (BS).
\f
Formfeed, Ctrl-l, ASCII code 12 (FF).
\n
Newline, Ctrl-j, ASCII code 10 (LF).
\r
Carriage return, Ctrl-m, ASCII code 13 (CR).
\t
Horizontal TAB, Ctrl-i, ASCII code 9 (HT).
\v
Vertical TAB, Ctrl-k, ASCII code 11 (VT).
\nnn
The octal value
nnn
, wherennn
stands for 1 to 3 digits between ‘0
’ and ‘7
’. For example, the code for the ASCII ESC (escape) character is ‘\033
’.\xhh…
The hexadecimal value
hh
, wherehh
stands for a sequence of hexadecimal digits (‘0
’–‘9
’, and either ‘A
’–‘F
’ or ‘a
’–‘f
’). A maximum of two digts are allowed after the ‘\x
’. Any further hexadecimal digits are treated as simple letters or numbers. (c.e.) (The ‘\x
’ escape sequence is not allowed in POSIX awk.)CAUTION: In ISO C, the escape sequence continues until the first nonhexadecimal digit is seen. For many years,
gawk
would continue incorporating hexadecimal digits into the value until a non-hexadecimal digit or the end of the string was encountered. However, using more than two hexadecimal digits produced undefined results. As of version 4.2, only two digits are processed.\/
A literal slash (should be used for regexp constants only). This sequence is used when you want to write a regexp constant that contains a slash (such as
/.*:\/home\/Gawk/docs/latest/:alnum:+:.*/
; the ‘Gawk/docs/latest/:alnum:
’ notation is discussed in Using Bracket Expressions). Because the regexp is delimited by slashes, you need to escape any slash that is part of the pattern, in order to tellawk
to keep processing the rest of the regexp.\"
A literal double quote (should be used for string constants only). This sequence is used when you want to write a string constant that contains a double quote (such as
"He said \"hi!\" to her."
). Because the string is delimited by double quotes, you need to escape any quote that is part of the string, in order to tellawk
to keep processing the rest of the string.
In gawk
, a number of additional two-character sequences that begin with a backslash have special meaning in regexps. See section gawk-Specific Regexp Operators.
In a regexp, a backslash before any character that is not in the previous list and not listed in gawk-Specific Regexp Operators means that the next character should be taken literally, even if it would normally be a regexp operator. For example, /a\+b/
matches the three characters ‘a+b
’.
For complete portability, do not use a backslash before any character not shown in the previous list or that is not an operator.
Backslash Before Regular Characters
If you place a backslash in a string constant before something that is not one of the characters previously listed, POSIX
|
To summarize:
- The escape sequences in the preceding list are always processed first, for both string constants and regexp constants. This happens very early, as soon as
awk
reads your program. gawk
processes both regexp constants and dynamic regexps (see section Using Dynamic Regexps), for the special operators listed ingawk
-Specific Regexp Operators.- A backslash before any other character means to treat that character literally.
Escape Sequences for Metacharacters
Suppose you use an octal or hexadecimal escape to represent a regexp metacharacter. (See Regular Expression Operators.) Does
Historically, such characters were taken literally. (d.c.) However, the POSIX standard indicates that they should be treated as real metacharacters, which is what |
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