this post was submitted on 18 Dec 2024
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zcat shouldn't error out if you try to zcat an uncompressed file, it should just output the damned file ! (lemmy.ml)
submitted 3 days ago by interdimensionalmeme@lemmy.ml to c/linux@lemmy.ml
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There I said it !

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[–] allywilson@lemmy.ml 17 points 3 days ago (2 children)

Yeah, it's a pain. Leads to bad one liners:

for i in $(ls); do zcat $i || cat $i; done

[–] MonkderVierte@lemmy.ml 11 points 3 days ago* (last edited 3 days ago) (2 children)

Btw, don't parse ls. Use find |while read -r instead.

find -maxdepth 1 -name "term" -print |while read -r file
   do zcat "$file" 2>/dev/null || cat "$file"
done
[–] allywilson@lemmy.ml 4 points 3 days ago (2 children)

Won't this cause cat to iterate through all files in the cwd once zcat encounters an issue, instead of just the specific file?

[–] LemoineFairclough@sh.itjust.works 2 points 3 days ago* (last edited 3 days ago)

You are correct. This probably produces something more similar to what you'd want the original command to do, but with better safely:

find -- . -type f -regex '^\./[^/]*$' -exec sh -c -- 'for file in "${@}"; do zcat "${file}" || cat "${file}" || exit; done' sh '{}' '+'

That assumes you want to interact with files with names like .hidden.txt.gz though. If you don't, and only intend to have a directory with regular files (as opposed to directories or symbolic links or other types of file), using this is much simpler and even safer, and avoids using files in a surprising order:

for i in *; do zcat -- "$i" || cat -- "$i" || exit; done

Of course, the real solution is to avoid using the Shell Command Language at all, and to carefully adapt any program to your particular problem as needed: https://sipb.mit.edu/doc/safe-shell/

[–] MonkderVierte@lemmy.ml 1 points 3 days ago

Yeah, i was tired and had $file there first, then saw that you wanted to cat all in directory. Still tired, but i think this works now.

[–] gnuhaut@lemmy.ml 1 points 2 days ago* (last edited 2 days ago) (1 children)

You can just do for f in * (or other shell glob), unless you need find's fancy search/filtering features.

The shell glob isn't just simpler, but also more robust, because it works also when the filename contains a newline; find .. | while read -r will crap out on that. Also apparently you want while IFS= read -r because otherwise read might trim whitespace.

If you want to avoid that problem with the newline and still use find, you can use find -exec or find -print0 .. | xargs -0, or find -print0 .. | while IFS= read -r -d ''. I think -print0 is not standard POSIX though.

[–] MonkderVierte@lemmy.ml 1 points 2 days ago (1 children)

because it works also when the filename contains a newline

Doesn't that depend on the shell?

[–] gnuhaut@lemmy.ml 1 points 2 days ago

I don't think so and have never heard that, but I could be wrong.

[–] interdimensionalmeme@lemmy.ml 5 points 3 days ago* (last edited 3 days ago)

Thanks !

But still we shouldn't have to resort to this !

~~Also, can't get the output through pipe~~

for i in $(ls); do zcat $i || cat $i; done | grep mysearchterm

~~this appears to work~~

~~find . -type f -print0 | xargs -0 -I{} sh -c 'zcat "{}" 2>/dev/null || cat "{}"' | grep "mysearchterm"~~

~~Still, that was a speed bump that I guess everyone dealing with mass compressed log files has to figure out on the fly because zcat can't read uncompressed files ! argg !!!~~

for i in $(ls); do zcat $i 2>/dev/null || cat $i; done | grep mysearchterm