Insert line after match using sed

Question

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

(-expressions (and the contents of -files) 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

A POSIX compliant one using the s command:

sed '/CLIENTSCRIPT="foo"/s/.*/&\
CLIENTSCRIPT2="hello"/' file

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.