Sed(1) one-liners | Hacker News Reader

Sed(1) one-liners

sed.sourceforge.net

50 pointsadamo13 comments

I don't see any use of the 'in-place' -i option.

My most useful one-liner:

        sed -i "s/pat/rep/g"   file

It means replace in-place all matches of pat with rep in file.

To make a backup of old file use -i.bak instead of -i where .bak would be the suffix of the backup file.

Option -i is not defined in POSIX sed. That's probably the reason author didn't include it in his list.

I have heard that it's GNU sed option only. (But can't currently say if it's 100% true.)

There's no reason why this functionality should be in sed when it can be implemented on its own and re-used. IIRC there's an an example script to for that in _The Unix Programming Environment_. Better to use sudo than have everything implement its own sudo-like functionality, etc.

See "UNIX Style, or cat -v Considered Harmful" by Rob Pike (http://harmful.cat-v.org/cat-v/) for a longer discussion of this.

In place operations have been implemented as a standalone utility: sponge from moreutils.

    sed 's/blah/foo/' file | sponge file

The irony

s stands for stream

there is no s in ed

I checked - it's pgs. 152-156. They call their utility "overwrite".

"...Many other commands could also use a -o command. For example, sed could edit a file in place: ... It would be impractical to modify all such commands to add the option. Furthermore, it would be bad design: it is better to centralize functions, as the shell does with the > operator."

Yes, thank you. Forgot to qualify that -i is only in GNU sed.

But I think it is in GNU sed for a reason -- it is a practical shortcut. The only thing I use sed for is to do search and replaces. If the command spanned 2 lines or had pipes and redirects a lot of people just wouldn't remember it.

I agree. It's very practical.

All pollution is practical, it takes discipline to dispose of waste properly.

man ed

If I'd want to edit in place I use ed

If I want to edit a stream I use sed

Equivalent perl one-liner (Perl regex may be more convenient):

   perl -e 's/pat/rep/g' -p -i file

-i.bak instead of -i works the same to create backups.

* explained http://www.catonmat.net/blog/sed-one-liners-explained-part-o...

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