sed error: "invalid reference \1 on `s' command's RHS"
RegexSedSubstitutionRegex Problem Overview
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
Regex Solutions
Solution 1 - Regex
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.
Solution 2 - Regex
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
Solution 3 - Regex
If the -r/--regexp-extended option is not provided, then the capturing parentheses must be escaped.
Solution 4 - Regex
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"