You can do "head -n 0" on Linux to mean "all lines".
Unix Commands I Abuse Every Day
31–40 of 108 posts
Re: Unix Commands I Abuse Every Day
#32Earlier quoted context omitted.
Would anyone mind doing me a favor by explaining xargs in more detail? I've tried learning it a couple times but I always seem to forget the primary situations in which it's useful. Thank you in advance!
Xargs takes a newline separated list and maps the list to a command. find ./ -name '*.log' | xargs rm Finds all log files and map them to 'rm' commands. e.g. if it finds system.log and rails.log it will run the command `rm system.log rails.log`. xargs will automatically do things like break up very long lists into multiple command calls so that it doesn't exceed the maximum number of arguments a command can have. Oth…
find ./ -name '*.log' | xargs rm
Almost everywhere I see xargs used, find ...-exec {} ; will work as well and find ...-exec {} + may work even better.
Re: Unix Commands I Abuse Every Day
#33My #1 abuse is xargs -n1. A lot of people like writing bash for loops, I will try and avoid that as much as possible, xargs -n1 is the bash equivalent of a call to 'map' in a functional language. For instance, let's say you want to create thumbnails of a bunch of jpegs: find images -name "*.jpg" | xargs -n1 -IF echo F F | sed -e 's/.jpg$/_thumb.jpg/' | xargs -n2 echo convert -geometry 200x Additionally, it's fully pa…
I use xargs a lot for refactoring work when I cannot simply use sed, e.g.
vim $(grep -lr foo | xargs)
and doing what I need to do on a file by file basis. Otherwise, for renaming functions and the like, I do a lot of:
find . -name foo_fn exec sed -i s/foo_fn/bar_fn/g '{}' \;
I generally love abusing bash. Just today I was asked about how to rename a bunch of files, specifically containing spaces, and came up with either of these two options:
find -name foo_bar -exec cp "'{}'"{,.bak} \;
and
for file in $(find -name foo_bar); do cp "$file"{,.bak}; done
Ultimately, the great thing is, if you learn CTRL-R, you can always search for these types of commands and modify them as necessary for the particular task at hand and not necessarily remember them. One I use all the time, to push git branches upstream is the following:
CTRL-R --set-
which gives me:
git push -f --set-upstream origin `git rev-parse --abbrev-ref HEAD`
This is entirely unique in my history, a common part of my workflow, and trivially searchable.
I also enjoy being able to perform something along the lines of:
vim $(bundle show foo-gem)
Re: Unix Commands I Abuse Every Day
#34Earlier quoted context omitted.
Does it really matter that you're starting an extra process?
it doesnt matter for a file of size 1kb. For a file of size 10Gb, every process matters. For the downvoters: please time how long it takes to do something like `cat $file | awk '{print $1}' ` and `awk <$file '{print $1}'`
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Re: Unix Commands I Abuse Every Day
#35Earlier quoted context omitted.
Xargs takes a newline separated list and maps the list to a command. find ./ -name '*.log' | xargs rm Finds all log files and map them to 'rm' commands. e.g. if it finds system.log and rails.log it will run the command `rm system.log rails.log`. xargs will automatically do things like break up very long lists into multiple command calls so that it doesn't exceed the maximum number of arguments a command can have. Oth…
find ./ -name '*.log' | xargs rm Only do that if you know exactly what '*.log' will expand to (i.e. don't use it in scripts and avoid using it on the command line). This is because the delimiter for xargs is a newline character, but filenames can have a newline character in them. This can lead to unexpected results. Almost everywhere I see xargs used, find ...-exec {} ; will work as well and find ...-exec {} + may wo…
find ./ -name '*.log' -print0 | xargs -0 rm
Re: Unix Commands I Abuse Every Day
#36My number one used command: grep -Hnri
This works really well with the suggested --color=always, because it highlights the line number, the filename and the separators in different colours.
Re: Unix Commands I Abuse Every Day
#37Earlier quoted context omitted.
I have long thought that some sort of zsh completion that detects that abuse of cat and converts it into the more appropriate `< file` might be a good idea. If it did it silently it probably wouldn't be worth it but if it actually preformed the substitution in front of you then it might help users get more comfortable with the carrot syntax.
Does it really matter that you're starting an extra process?
No.
It is pretty much just a matter of principle.
Re: Unix Commands I Abuse Every Day
#38Earlier quoted context omitted.
If you like xargs, but want jobs to execute in parallel, you may enjoy GNU parallel. Your trivial example: find images -name "*.jpg" | parallel convert -geometry 200x {} {.}_thumb.jpg
xargs --max-procs=#
However, unlike xargs, GNU Parallel gives you a guarantee on the order of the output. From the man page:
GNU parallel makes sure output from the commands is the same output as
you would get had you run the commands sequentially. This makes it
possible to use output from GNU parallel as input for other programs.Re: Unix Commands I Abuse Every Day
#39Nice unix commands
Re: Unix Commands I Abuse Every Day
#40You can do "head -n 0" on Linux to mean "all lines". No you can't.
`head -n 99999` seems like a weird way to do it anyway. Wouldn't it make more sense to do `tail -n +1`? The output is the same from both commands, but `tail` doesn't require you to assume arbitrary limits.
Honest question, btw. I'm relatively inexperienced with Linux, and I certainly haven't used BSD. I'd appreciate any critiques you may have to offer.