How to UNCOMMENT a line that contains a specific string using Sed?
BashAwkSedBash Problem Overview
The lines in the file :
-A INPUT -m state --state NEW -m tcp -p tcp --dport 2000 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 2001 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 2002 -j ACCEPT
to comment out let's say the line that contains
2001
i can simply run this SED command:
sed -i '/ 2001 /s/^/#/' file
but now how do i revert back ?
as in uncomment that same line ?
i tried
sed -i '/ 2001 /s/^//' file
that does not work.
Bash Solutions
Solution 1 - Bash
Yes, to comment line containing specific string with sed, simply do:
sed -i '/<pattern>/s/^/#/g' file
And to uncomment it:
sed -i '/<pattern>/s/^#//g' file
In your case:
sed -i '/2001/s/^/#/g' file (to comment out)
sed -i '/2001/s/^#//g' file (to uncomment)
Option "g" at the end means global change. If you want to change only a single instance of pattern, just skip this.
Solution 2 - Bash
Try this sed
command,
sed -i '/^#.* 2001 /s/^#//' file
Solution 3 - Bash
To complement @Avinash Raj's helpful answer with a more generic, POSIX-compliant solution.
- Toggles commenting of lines that match a specifiable string that must occur as a separate word anywhere on the line.
- The comment character (string) is also specifiable.
Note that the solution is awk
-based, because a robust portable solution with sed
is virtually impossible due to the limitations of POSIX' basic regular expressions.
awk -v commentId='#' -v word='2001' '
$0 ~ "(^|[[:punct:][:space:]])" word "($|[[:punct:][:space:]])" {
if (match($0, "^[[:space:]]*" commentId))
$0 = substr($0, RSTART + RLENGTH)
else
$0 = commentId $0
}
{ print }
' file > tmpfile.$$ && mv tmpfile.$$ file
(^|[[:punct:][:space:]])
and($|[[:punct:][:space:]])
are the POSIX extended regex equivalents of the\<
and\>
word-boundary assertions known from other regex dialects.- Whitespace after the comment char is preserved, but not before it.
- When prepending the comment char to a line, it is directly prepended, without whitespace.
- Thus, if you only toggle comments with this solution, all whitespace is preserved.
- POSIX
awk
doesn't offer in-place updating (neither does POSIXsed
, incidentally), hence the output is first captured in a temporary file and that file then replaces the original on success.
Solution 4 - Bash
Quick example of how to comment and uncomment a line in a file.
Sample file :
umask 027
TMOUT=600
Lets now backup the file (just for laughs) and comment out and un comment:
# backup file (because we should always do this)
cp /etc/bash.bashrc /etc/bash.bashrc.$(date '+%Y-%m-%d,%H:%M:%S')
# original: TMOUT=600 , result :# TMOUT=600
sed -i '/[^#]/ s/\(^TMOUT=600.*$\)/#\ \1/' /etc/bash.bashrc
# original # TMOUT=600 ,result :TMOUT=600
sed -i '/^#.*TMOUT=600.*$/s/^#\ //' /etc/bash.bashrc
Solution 5 - Bash
For mac, which doesn't support standard sed parameters, this would remove the hashtag
sed -i "" "/.*#.*d\/docker-php-ext-xdebug\.ini.*/s/^#//g" docker-compose.yml