Unix Commands I Abuse Every Day

Post by ralph » Thu, Sep 06, 2012, 8:46 AM UTC

sonnym wrote: post #33

andrewvc wrote: post #2

My #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 eit…

    vim $(grep -lr foo | xargs)

    vim $(grep -lr foo .)

    find . -name foo_fn exec sed -i s/foo_fn/bar_fn/g '{}' \;

    find -name '*.[ch]' -exec sed -i 's/\/bar/g' {} +

Post by ralph » Thu, Sep 06, 2012, 8:57 AM UTC

gnaritas wrote: post #35

planckscnst wrote: post #32

Earlier quoted context omitted.

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 Fixes that issue and xargs is far more efficient, it doesn't launch a new process for each line like exec does, but far more importantly, xargs is generalizable to all commands so you only have to learn it once; exec is just an ugly hack on find, you can't generalize it across all commands; xargs is much more unixy.

    find -name '*.log' -delete

Post by ralph » Thu, Sep 06, 2012, 9:07 AM UTC

a3_nm wrote: post #64

jlgreco wrote: post #11

Earlier 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.

Interestingly, there are some circumstances where you actually want "cat file | program" and not "program < file". The case I have in mind is when file is actually a named FIFO which was not opened for writing. If you use cat, program will still run and only reads to stdin will block (but it can perform other things, possibly in different threads). If you use '<', opening stdin will block and program will probably bl…

Post by CGamesPlay » Thu, Sep 06, 2012, 9:12 AM UTC

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