103 lines
2.8 KiB
Markdown
103 lines
2.8 KiB
Markdown
---
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title: "bash_tricks"
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tags: [ "Documentation", "System" ]
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---
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# Automatic mp3 Tagging
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/u/OneTurnMore on Reddit:
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> !/usr/bin/env bash
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> IFS=$'\n'
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> for f in $(find . -type f); do
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> id3tool $f -t $(basename $f | cut -d- -f3 | sed 's/\.[^\,]*$//')
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> done
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One can also use
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> sed s/\,[^\.]*$//
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... in order to avoid multiple full stops messing up syntax.
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We can use `\.` as a literal full stop.
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`[^ ]` means anything other than the containing character, so `[^\.]` would mean `anything other than a full stop'.
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`*` in sed means this character is repeated any number of times, including 0, so files with no `.` character would still be processed fine.
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`$` means `end of the line'.
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Apparently sed uses `regex, not globing'.
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Regular expressions (``regex'') looks for patterns and is used with find and grep. It interprets `*' as a wildcard, `?' as a single-character wildcard, and [12,1,2] as characters matching one of a set (in this case, `12 or 1 or 2 but not 21'].
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If the shell is set to find file ``a*b.txt'' then it will pass this first to regex, and hit items like `aab.txt' and `abb.txt'. If it finds nothing, it'll then use globbing, and interpret `a*b.txt' literally.
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# Alias Expansion
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> echo '"\C- ": shell-expand-line' >> ~/.inputrc
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Reload bash, and you can use Ctrl+Space to expand an alias.
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Type in `ll` (or any alias), then Ctrl+Space.
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# Automatic Renaming
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There are a bunch of files:
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* Column CV.aux
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* Column CV.log
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* Column CV.out
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* Column CV.pdf
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* Column CV.tex
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* tccv.cls
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Goal: swap the word ``Column'' for ``Malin'' in all files.
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> IFS=$'\n'
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> for f in $(find . -name "Col*"); do
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> mv "$f" $(echo "$f" | sed s/Column/Malin/)
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> done
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IFS is the field separator. This is required to denote the different files as marked by a new line, and not the spaces.
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# Arguments and Input
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The `rm' program takes arguments, but not `stdin' from a keyboard, and therefore programs cannot pipe results into rm.
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That said, we can sometimes pipe into rm with `xargs rm' to turn the stdin into an argument. For example, if we have a list of files called `list.txt' then we could use cat as so:
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> cat list.txt | xargs rm
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... *However*, this wouldn't work if spaces were included, as rm would take everything literally.
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# Numbers
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Add number to variables with:
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* > let "var=var+1"
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* > let "var+=1"
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* > let "var++"
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* > ((++var))
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* > ((var=var+1))
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* > ((var+=1))
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* > var=$(expr $var + 1)
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((n--)) works identically.
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# Finding Duplicate Files
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> find . -type f -exec md5sum '{}' ';' | sort | uniq --all-repeated=separate -w 15 > all-files.txt
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... add blank line to top of first file.
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> awk '/^$/{getline;print;}' all-files.txt > uniq.txt
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> diff all-files.txt uniq.txt | grep '/' | cut -d '.' -f 2,3,4,5 | sed 's#/##' | sed 's/ /\\ /g' | xargs rm
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Output random characters.
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> cat /dev/urandom | tr -cd [:alnum:] | dd bs=1 count=200 status=none && echo
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