For the past 30 years or so, my brain always tells me to type "last" instead of "tail". This usually results in some kind of "Permission denied" message that confuses me for a few seconds.
Yes, but it shows information about recent/current logins and requires access a file called wtmp (or something like that, off the top of my head), and that requires privileged access.
My usual use case where I mix it up is looking at a log file and and I just want to see the last few entries. So my brain 🧠 tells my fingers to type "last logfile", and when I get the permission message it tells my mouth to go, "Doh!".
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).
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.
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
That's fair. I'd usually just use less and drop to the end. My use cases would always need the older log before a newer log though because that's the start of the problem. At least that's how I operate.
61 replies
I was today's years old to finally notice the cat-head-tail thing...
But it also just recently dawned upon me why pacman has those weird "c" as progress indicators...
I'm not a smart man...
For the past 30 years or so, my brain always tells me to type "last" instead of "tail". This usually results in some kind of "Permission denied" message that confuses me for a few seconds.
there's a last command? just knowing that.
Yes, but it shows information about recent/current logins and requires access a file called wtmp (or something like that, off the top of my head), and that requires privileged access.
My usual use case where I mix it up is looking at a log file and and I just want to see the last few entries. So my brain 🧠 tells my fingers to type "last logfile", and when I get the permission message it tells my mouth to go, "Doh!".
yeah I looked it up
this will be handy
Bat is my favorite command to date.
catis misunderstood a lot. The purpose of cat is to combine multiple files together (it's literally short for "concatenate"), likecat *.logto 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:
For
head,tail,grepand some other commands, you can just pass in the file name directly as an argument (e.g.grep whatever foo.txt).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
You'll see
cat FILE |all the time because it's just a natural start to a pipeline. Youcat FILEto see the content unfiltered before filtering it with further commands.Fair, but in general I find it way more useful to use cat for piping.
In most cases I'll do something like
This gets more complicated if the file is at the end of the command.
I don't know why anybody would disagree with this. It's a very clean way of putting it.
It wouldn't be at the end, since you'd still be piping into
programAnd
<file program | grep | cutworks tooOh, thanks! Didn't know that
Thanks - I didn't know this either!
If I just want to look at the file, is there a better way than
cat foo.txt? I guess I can't just do< foo.txtIf it's really long, I use
less, because it breaks it up into navigable pages instead of filling your entire buffer. :)Never knew about just using < though! Cool!
Admittedly I still use
catfor this.This also works too, but it's more verbose:
It's mentioned in the Bash man pages:
EDIT: I was just informed that simply
<foo.txtworks too.how in the world is this not a useless use of echo and equivalent to
<foo.txtOK, TIL you can just do
<foo.txt. I didn't think that worked. Thanks!So close! you have to do
cat < foo.txt:-) (/s)You can use
less. There are also specialized ones for that purpose like bat.I still like doing
cat file.txt | grep thingbecause I often re-run it to find something else likecat 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 thingalso works.is it more obtuse
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.
I would.
I'd be careful of jokes, sure, but geeks often can't help have real discussions. Like in this very thread
tac
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.
That's fair. I'd usually just use less and drop to the end. My use cases would always need the older log before a newer log though because that's the start of the problem. At least that's how I operate.
Another all-time favorite:
I've been using a slightly customized bash-cat for years now. Still makes me smile when I see it
yeah I just checked it out it's cute
last commit message: "Shorter Cat with added Tail." 👍
tacis a cat but faced the other wayohhh let me check it out lol
I always thought it's
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
whereis cat?
which catwhatis cat?
man catlocate cat
strace catrtfm
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??
In order of approachability:
Man pages.
Also Arch Wiki.
Also excellent books by NoStarch Press.
... Or did I miss a joke? Hehe