For some reason I can't seem to find a straightforward answer to this and I'm on a bit of a time crunch at the moment. How would I go about inserting a choice line of text after the first line matching a specific string using the sed
command. I have ...
CLIENTSCRIPT="foo"
CLIENTFILE="bar"
And I want insert a line after the CLIENTSCRIPT=
line resulting in ...
CLIENTSCRIPT="foo"
CLIENTSCRIPT2="hello"
CLIENTFILE="bar"
Try doing this using GNU sed:
sed '/CLIENTSCRIPT="foo"/a CLIENTSCRIPT2="hello"' file
if you want to substitute in-place, use
sed -i '/CLIENTSCRIPT="foo"/a CLIENTSCRIPT2="hello"' file
Output
CLIENTSCRIPT="foo"
CLIENTSCRIPT2="hello"
CLIENTFILE="bar"
Doc
see sed doc and search \a (append)
Note the standard sed
syntax (as in POSIX, so supported by all conforming sed
implementations around (GNU, OS/X, BSD, Solaris...)):
sed '/CLIENTSCRIPT=/a\
CLIENTSCRIPT2="hello"' file
Or on one line:
sed -e '/CLIENTSCRIPT=/a\' -e 'CLIENTSCRIPT2="hello"' file
(-e
xpressions (and the contents of -f
iles) are joined with newlines to make up the sed script sed
interprets).
The -i
option for in-place editing is also a GNU extension, some other implementations (like FreeBSD's) support -i ''
for that.
Alternatively, for portability, you can use perl
instead:
perl -pi -e '$_ .= qq(CLIENTSCRIPT2="hello"\n) if /CLIENTSCRIPT=/' file
Or you could use ed
or ex
:
printf '%s\n' /CLIENTSCRIPT=/a 'CLIENTSCRIPT2="hello"' . w q | ex -s file
sed -e '/CLIENTSCRIPT=/a\' -e 'CLIENTSCRIPT2="hello"' file
escapes the quote at the end of the first parameter and breaks the command.
csh
or rc
family, '...'
are strong quotes inside which backslash is not special. The only exception that I know is the fish
shell.
sed
not being POSIX compliant here. That makes my statement about it being portable incorrect (for the one line variant). I'll ask the opengroup for confirmation if it's indeed a non-conformance or a misinterpretation of the standard on my part.
printf...ex
version. This works like charm!
A POSIX compliant one using the s
command:
sed '/CLIENTSCRIPT="foo"/s/.*/&\
CLIENTSCRIPT2="hello"/' file
sed -e '/.../s/$/\' -e 'CLI.../'
which would avoid problems with lines that contain byte sequences not forming valid characters.
Sed command that works on MacOS (at least, OS 10) and Unix alike (ie. doesn't require gnu sed like Gilles' (currently accepted) one does):
sed -e '/CLIENTSCRIPT="foo"/a\'$'\n''CLIENTSCRIPT2="hello"' file
This works in bash and maybe other shells too that know the $'\n' evaluation quote style. Everything can be on one line and work in older/POSIX sed commands. If there might be multiple lines matching the CLIENTSCRIPT="foo" (or your equivalent) and you wish to only add the extra line the first time, you can rework it as follows:
sed -e '/^ *CLIENTSCRIPT="foo"/b ins' -e b -e ':ins' -e 'a\'$'\n''CLIENTSCRIPT2="hello"' -e ': done' -e 'n;b done' file
(this creates a loop after the line insertion code that just cycles through the rest of the file, never getting back to the first sed command again).
You might notice I added a '^ *' to the matching pattern in case that line shows up in a comment, say, or is indented. Its not 100% perfect but covers some other situations likely to be common. Adjust as required...
These two solutions also get round the problem (for the generic solution to adding a line) that if your new inserted line contains unescaped backslashes or ampersands they will be interpreted by sed and likely not come out the same, just like the \n
is - eg. \0
would be the first line matched. Especially handy if you're adding a line that comes from a variable where you'd otherwise have to escape everything first using ${var//} before, or another sed statement etc.
This solution is a little less messy in scripts (that quoting and \n is not easy to read though), when you don't want to put the replacement text for the a command at the start of a line if say, in a function with indented lines. I've taken advantage that $'\n' is evaluated to a newline by the shell, its not in regular '\n' single-quoted values.
Its getting long enough though that I think perl/even awk might win due to being more readable.
s/CLIENTSCRIPT="foo"/&\
[Enter] CLIENTSCRIPT2="hello"/
. The backslash has to be the very last character on the line (no whitespace after it), contrary to how it looks in this comment.
s///
, as well as those in the a
and i
commands can be "escaped," using the same method I describe in my comment above.
Maybe a bit late to post an answer for this, but I found some of the above solutions a bit cumbersome.
I tried simple string replacement in sed and it worked:
sed 's/CLIENTSCRIPT="foo"/&\nCLIENTSCRIPT2="hello"/' file
& sign reflects the matched string, and then you add \n and the new line.
As mentioned, if you want to do it in-place:
sed -i 's/CLIENTSCRIPT="foo"/&\nCLIENTSCRIPT2="hello"/' file
Another thing. You can match using an expression:
sed -i 's/CLIENTSCRIPT=.*/&\nCLIENTSCRIPT2="hello"/' file
Hope this helps someone
\n
in the replacement string. Plain-vanilla (POSIX) sed
does not understand \n
in the replacement string, however, so this won't work on BSD or macOS—unless you've installed GNU sed somehow. With vanilla sed you can embed newlines by "escaping" them—that is, ending the line with a backslash, then pressing [Enter] (reference, under the heading for [2addr]s/BRE/replacement/flags
). This means your sed command has to span multiple lines in the terminal.
The awk variant :
awk '1;/CLIENTSCRIPT=/{print "CLIENTSCRIPT2=\"hello\""}' file
1;
, see Why does “1” in awk print the current line?
I had a similar task, and was not able to get the above perl solution to work.
Here is my solution:
perl -i -pe "BEGIN{undef $/;} s/^\[mysqld\]$/[mysqld]\n\ncollation-server = utf8_unicode_ci\n/sgm" /etc/mysql/my.cnf
Explanation:
Uses a regular expression to search for a line in my /etc/mysql/my.cnf file that contained only [mysqld]
and replaced it with
[mysqld] collation-server = utf8_unicode_ci
effectively adding the collation-server = utf8_unicode_ci
line after the line containing [mysqld]
.
I had to do this recently as well for both Mac and Linux OS's and after browsing through many posts and trying many things out, in my particular opinion I never got to where I wanted to which is: a simple enough to understand solution using well known and standard commands with simple patterns, one liner, portable, expandable to add in more constraints. Then I tried to looked at it with a different perspective, that's when I realized i could do without the "one liner" option if a "2-liner" met the rest of my criteria. At the end I came up with this solution I like that works in both Ubuntu and Mac which i wanted to share with everyone:
insertLine=$(( $(grep -n "foo" sample.txt | cut -f1 -d: | head -1) + 1 ))
sed -i -e "$insertLine"' i\'$'\n''bar'$'\n' sample.txt
In first command, grep looks for line numbers containing "foo", cut/head selects 1st occurrence, and the arithmetic op increments that first occurrence line number by 1 since I want to insert after the occurrence. In second command, it's an in-place file edit, "i" for inserting: an ansi-c quoting new line, "bar", then another new line. The result is adding a new line containing "bar" after the "foo" line. Each of these 2 commands can be expanded to more complex operations and matching.
Success story sharing
sed
. That's not standardsed
syntax and won't work with any othersed
implementation.