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Random note. The most commonly "abused" Unix command is cat. The name is short for "concatenate", and its intended purpose was originally to combine 2 or more files at once. Therefore every time you use it to spool one file into a pipeline, that is technically an abuse!
You can do "head -n 0" on Linux to mean "all lines". No you can't.
The '-' between -n and 0 means "all but the last 0 lines".
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…
Furthermore, instead of the pipe to sed and extra xargs, it might be clearer and simpler to do something like:
zargs -n 1 **/*.jpg -- make-thumb
convert -geometry 200x $1 ${1%%.jpg}_thumb.jpg
zargs -n 1 **/*.jpg | vipe > myscript
One final trick is for when you need to do in-place image manipulation. Instead of using "convert", you can use another ImageMagick command: "mogrify". It will overwrite the original file with the modified file. Of course, you should be very careful with it.
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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.
Random note. The most commonly "abused" Unix command is cat. The name is short for "concatenate", and its intended purpose was originally to combine 2 or more files at once. Therefore every time you use it to spool one file into a pipeline, that is technically an abuse!
Since everything's a file* in UNIX (and ilk,) it's actually not an abuse.
* Pedantic variations such as "everything's a bytestream" or "everything's a file descriptor" notwithstanding.
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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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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}'`
So the two are different because awk's call to read() is effectively the same as a read directly from a file, whereas copying is taking place through the pipe with the pipeline approach?
time read
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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.
> carrot syntax Heh. Be careful with this, though: ^ is the caret (note spelling) according to most sources of information about these things. Random Fun Geekery Time: Back in the Before-Before, the grapheme in ASCII at the codepoint ^ is now was an up-arrow character, which is why BASIC uses ^ for exponentiation even though FORTRAN, which came first and which early BASIC dialects greatly copied, uses . These days, ↑…
That is, two asterisks in a row.