[SOLVED] what is @@ in sed?

centguy · 04-10-2023, 10:30 PM

This works:

Quote:

ls -1 *py | sed s@.py@@g

This lists out all files with .py extension.
Then it pulls out stem if the file name is stem.py.

But how to interpret this cryptic @@?

It seems @ is holding the stem, but why @@? Wouldn't it
give stemstem?

Turbocapitalist · 04-10-2023, 10:45 PM

The basic syntax is s/// with the slash / being a delimiter between the substitution pattern being sought and the replacement pattern. However, you can use anything. These are all the same:

Code:

ls -1 *py | sed s/.py//
ls -1 *py | sed s|.py||
ls -1 *py | sed s#.py##
ls -1 *py | sed 's!.py!!' 
ls -1 *py | sed sa.pyaa 
ls -1 *py | sed sb.pybb 
# etc

You can do similarly with the regular pattern search // too.

Code:

ls -1 | sed -n -e '/py$/p'
ls -1 | sed -n -e '\|py$|p'
ls -1 | sed -n -e '\#py$#p'
ls -1 | sed -n -e '\!py$!p'
# etc

See "man sed" and scroll down to \cregexpc unde "Addresses"

evo2 · 04-10-2023, 10:48 PM

In this case "@" is being used as the delimiter for sed which is doing a search "s" for the string ".py" (sring between the 1st and 2nd delimiters) and replacing globally "g" with nothing (string between the 2nd and 3rd delimiters).

Evo2.

michaelk · 04-10-2023, 10:51 PM

@ is used as the separator instead of /

Quote:

ls -1 *py | sed s/.py//g

Does this make it easier to understand? s substitute, global replace. I assume the @ is used since the command might contain paths with /s

Too late...

centguy · 04-11-2023, 12:33 AM

ok. now I conclude the "g" (for global)
is pretty useless 99.999% of the time in this case (nobody will name a file stem.py.py or something like it)

To summarize:

ls -1 *py | sed s@.py@@

means look for .py and replace it with nothing, essentially removing .py from the string.

Now I learned that one could use a delimiter other than / (what I used to know!)

Thanks for the prompt replies and the fruitful comments!

pan64 · 04-11-2023, 12:54 AM

Just for curiosity: sed will remove the first .py, not the last one.

Code:

echo filename.py.a.py | sed s@.py@@

chrism01 · 04-12-2023, 12:44 AM

See this https://en.wikipedia.org/wiki/Leanin...hpick_syndrome

MadeInGermany · 04-17-2023, 09:01 AM

Perhaps you can consolidate to one RE

Code:

ls | sed -n 's/[.]py$//p'