Linux SED command syntax with escapes

Question

I am trying to replace a script call with a script call from a sub directory.

For example, originally I had ./output.sh in my script to call the output.sh script in the current directory.

I want to replace ./output.sh with ../output.sh so that it calls output.sh in the parent directory.

I tried

sed -i -e 's/../\output.sh/./\output.sh/g' scriptName.sh

This returns with

char 17: unknown option to 's'

Any help with the sed escape character syntax would be great.

To replace "./output.sh" with "../output.sh", you can try `sed 's@\([^.]\)\./output\.sh@\1../output.sh@g` (this won't match entries at the beginning of the line, but gives you a good start on a solution). But this is not the correct way to solve your problem! — William Pursell, Jan 05 '17 at 17:35
Or [sed search and replace strings containing /](http://stackoverflow.com/q/10309968/3266847) or [Use slashes in sed replace](http://stackoverflow.com/q/5864146/3266847) — Benjamin W., Jan 05 '17 at 18:07

score 1 · Answer 1 · answered Jan 06 '17 at 02:39

Sed is bad at this; you'll risk turning an already existing ../output.sh into .../output.sh if you're not careful.

This is the best sed can do:

sed -i 's@output\.sh@../$@g' scriptName.sh

(I'm using @ in place of / so that there are no forward slashes to escape. Sed accepts any punctuation character in place of forward slash.)

Note that this will convert ../output.sh to ../../output.sh but at least it doesn't create that triple-dot error.

Instead, try perl:

perl -pie 's@(?<!\.\./)(output\.sh\b)@../$1@g' scriptName.sh

This uses a negative look-behind to ensure it doesn't traverse to the parent's parent. It also allows using \b to denote a word break just in case you have something like output.shelf somewhere.

Michał Kosmulski · Answer 2 · 2017-01-06T08:45:09.397

The slash character is special in sed's s command if you formulate it as s/something/replacement/flags, so the slashes in your file paths cause the error. Fortunately, you can use any other character right after s, for example s@something@replacement@flags. So, replacing the command with s@\./output.sh@../output.sh@g should do the trick.

Note two additional changes: you have to escape the dot in first expression since it's also a special character in regex and you also got reversed order of search expression and replacement (thanks charli for noticing this). You don't need the backslashes before o characters, either.

Alternatively, you can use / after s but escape the literal slashes you want to replace by preceding them with backslashes: s/\.\/output.sh/..\/\output.sh/g. It seems in your code you tried to use this solution but put the backslashes after instead of before the slashes.

If you don't escape the dots, it can replace strings as `directory/output.sh` to `director./output.sh`. Also, the question is to change from `./output.sh` to `../output.sh`, your patterns are reversed. — charli, Jan 05 '17 at 17:47
@charli Thanks for pointing this out. There were so many issues with the original expression I just skimmed over them without noticing. — Michał Kosmulski, Jan 06 '17 at 08:46

score 0 · Answer 3 · answered Jan 05 '17 at 17:40

This would do the trick. Substitutes every appearance of ./output.sh for ../output.sh :

sed 's/\.\/output\.sh/\.\.\/output\.sh/g' scriptName.sh

The escape character is \. You should use it to escape:

Every dot .. The dot is used as any character in regex.
Every slash /. The slash character is used as delimiter between regex on the scommand.

Linux SED command syntax with escapes

3 Answers3