sed error: "invalid reference \1 on `s' command's RHS"
I run several substitution commands as the core of a colorize script for maven. One of the sed commands uses a regular expression which works find in the shell as discussed here. The current (not working) implementation can be found here.
When I include one of the variants of the command into the script different behavior occurs:
Variant 1:
$ sed -re "s/([a-zA-Z0-9./\\ :-]+)/\1/g"
Adapted to the script:
-re "s/WARNING: ([a-zA-Z0-9./\\ :-]+)/${warn}WARNING: \1${c_end}/g" \
Error: The shell outputs the same information as if I would type $ sed. Strange!?
Variant 2:
$ sed -e "s/\([a-zA-Z0-9./\\ :-]\+\)/\1/g"
Adapted to the script:
-e "s/WARNING: \([a-zA-Z0-9./\\ :-]\+\)/${warn}WARNING: \1${c_end}/g" \
Error:
sed: -e expression #7, char 59: invalid reference \1 on `s' command's RHS
-i (edit in place option) with -re, resulting in -ire (so that -i was consuming the re fragment as its SUFFIX argument and hence the extended regex mode was not being enabled); changing it to -i -re fixed the issue.
' and double quotes " are treated slightly different, especially when interpreting $vars. For example: sudo sh -c "sed -r -i 's/(^.+_supplicant.conf)/\1${MTXT}/' /etc/network/interfaces" works, but: sudo sh -c 'sed -r -i "s/(^.+_supplicant.conf)/\1${MTXT}/" /etc/network/interfaces' does not.
Don't you need to actually capture for that to work? i.e. for variant #2:
-r -e "s/WARNING: (\([a-zA-Z0-9./\\ :-]\+\))/${warn}WARNING: \1${c_end}/g" \
(Note: untested)
Without the -r argument back-references (like \1) won't work unless each parenthesis is escaped with a \ character.
With -r, argument back-references (like \1) won't work unless the parenthesis are NOT escaped.
This error is common for parentheses that are not escaped. Escape them and try again.
For example:
/^$/b
:loop
$!{
N
/\n$/!b loop
}
s/\n(.)/\1/g
Should be escaped with backslashes before each parenthesis:
/^$/b
:loop
$!{
N
/\n$/!b loop
}
s/\n\(.\)/\1/g
-r you don't have to escape the parentheses.
If the -r/--regexp-extended option is not provided, then the capturing parentheses must be escaped.
You need escape the / after the .
sed -e "s/\([a-zA-Z0-9.\/\\ :-]\+\)/\1/g"
Or if you don't want to worry about escaping, use |
sed -e "s|\([a-zA-Z0-9./\\ :-]\+\)|\1|g"
EDIT:
sed -e "s|WARNING: \([a-zA-Z0-9.-/\\ :]+\)|${warn}WARNING: \1${c_end}|g"
sed: -e expression #7, char 58: Invalid range end. @Denis' answer works.
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-roption to sed appears to be necessary for the back-reference to work. E.gsed -e 's/([[:digit:]])/is a digit/'works butsed -e 's/([[:digit:]])/\1 is a digit/produces the original error without-rto sed. NOTE: the first invocation of sed searches for a literal(<digit>)and is not a capture group.-ireinstead of use-ri. Order matters :-)-r, --regexp-extended=use extended regular expressions in the script.In most current versions the-Eand-rboth can be used. Extended as opposed to basic.