Comment by jdbartee
3 years ago
Speaking for myself, the first form is more natural- even if it’s a useless cat, because I’m always cat-ing files to see their structure. Then progressively tacking on different transforms. And then finally putting it in whatever I want as output.
It’s so ingrained, I’m more likely than not to just write it out that way even when I know exactly what I’m doing from the onset.
Yes, this iterative procedure is often why "useless" cats get put into it. It's a very effective way of processing regular text information.
e.g.
I need to grab some info from textfile.txt to use as arguments to a function.
cat textfile.txt
looks like its comma delimited.
cat textfile.txt | cut -d, -f 2-5
ah, its the third and fourth column i need
cat textfile.txt | cut -d, -f 3-4 | grep '123456'
perfect
cat textfile.txt | cut -d, -f 3-4 | grep 123456 | tr , ' '
myfunc $(cat textfile.txt | cut -d, -f 3-4 | grep 123456 | tr , ' ')
> cat textfile.txt
> looks like its comma delimited.
Interesting; why wouldn't you use `head`? Who knows how big textfile.txt is?
generally, speaking, if you don't have an idea of how big the file is, or it would take up too much real-estate on your terminal window, sure. 100%. It was just an example.
lot's of times we sort of know what we are working with, but don't remember the particulars especially
Don't forget to pipe head into 'cat -v'... that text file could contain _anything_!
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`file` will tell you too
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I've been using bat as a cat replacement for a while now. It includes paging, syntax highlighting, line numbers, and is generally very performant.
https://github.com/sharkdp/bat
As a scientist who cares about reproducibility, the big difference between the "useless cat" and providing the input file name on the command line is that, in the latter case, the program can capture that file name and reproduce it. That is harder when using stdin.
Many of my programs and scripts start output with the line: # cmd arg1 arg2 arg3 ...
and simply echo back lines that start with '#'. That way, I have an internal record of the program that was run and the data file that was read (as well as previous parts of the analysis chain).
And, 'R' ignores lines starting with '#', so the record is there, but does not affect later analyses.
You could consider
If you're using zsh, you can just replace any instance of
with
For bash, this only works if you have at least one `|`.
I did this last time I saw it come up and was surprised! Doing it makes perfect sense in hindsight. Neato!