tac
this post was submitted on 03 Aug 2026
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I've always wondered what a good use case for tac would be...
Reverse chronological order, mostly
tac log.txt |head # would give you newest first
no good for sort because sort already supports -r
no need it for tail on large files because tail already skips to the end.
I do a lot of impromptu bash to sus crap out of logs.
when you're balls deep in
cat log|grep -v foo| rev|cut -f 1-3 -d \ | |rev
Sometimes tac comes in clutch.
I always thought it's
head | cat | tail
It, of course, waits for an input, which brings up the one and only question...
Have you fed your cat?
of course look meow meow so loud
cat is misunderstood a lot. The purpose of cat is to combine multiple files together (it's literally short for "concatenate"), like cat *.log to combine all log files together.
If you're just using it for a single file, then you should just redirect the file to stdin. These two command lines behave similarly:
cat foo.txt | some-command
some-command < foo.txt
For head, tail, grep and some other commands, you can just pass in the file name directly as an argument (e.g. grep whatever foo.txt).
Fair, but in general I find it way more useful to use cat for piping.
In most cases I'll do something like
cat file | program
cat file | program | grep
cat file | program | grep | cut
This gets more complicated if the file is at the end of the command.
It wouldn't be at the end, since you'd still be piping into program
program <file | grep | cut
And <file program | grep | cut works too
Thanks - I didn't know this either!
Oh, thanks! Didn't know that
Also known as cat abuse.
awww what's a cat without a head and a tail?
I guess depending on your interpretation of without it could either be "cat" or "a".
A kernel?
uhmm no
I still like doing cat file.txt | grep thing because I often re-run it to find something else like cat file.txt | grep thing2 - and if I do that with grep, the pattern sits awkwardly in the middle instead of at the end
< file.txt grep thing also works.
You'll see cat FILE | all the time because it's just a natural start to a pipeline. You cat FILE to see the content unfiltered before filtering it with further commands.
it’s just a natural start to a pipeline
If it just want to look at the file, is there a better way than cat foo.txt? I guess I can't just do < foo.txt
Admittedly I still use cat for this.
This also works too, but it's more verbose:
echo "$(<foo.txt)"
It's mentioned in the Bash man pages:
The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).
So close! you have to do cat < foo.txt :-) (/s)
yeah sure but the command is literally written for the humor.
I know, but I just wanted to mention this since a lot of new Linux users end up using cat this way :)
Is there any downside?
ohhh but it's all humor that's the point of the post.
I mean as a new Linux user, I won't take anything from a humor group seriously.
Another all-time favorite:
$ man woman
No manual entry for woman
$ touch woman
touch: cannot touch 'woman': Permission denied
whereis cat?
which cat
whatis cat?
man cat
locate cat
I've been using a slightly customized bash-cat for years now. Still makes me smile when I see it
last commit message: "Shorter Cat with added Tail." 👍
yeah I just checked it out it's cute
tac is a cat but faced the other way
ohhh let me check it out lol
rtfm
Be careful now, 2000/2010 Linux terminology can be taken as an insult in 2026. /s
I’m tired of this stupid coddling bullshit with the influx of new Linux users. If you can’t read don’t use Linux. Simple. 😂
But wheres the manual??
man which
