arnaudjuracek/bash-snippets.md

## bash-snippets.md

      
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              bash-snippets.md
            
          
    bash snippets


Personnal collection of useful bash snippets.


Table of Contents


Basics

Repeat last command
Repeat last argument
Expand wildcards
Variable expansion
Array and list
Loops
Sequential vs parallel loop execution


File manipulation

Append timestamp
Lowercase a batch of files
Batch change file extension in any depth
Delete files under 1kB
Clean up SVGs and convert to php file
Pipe a list of paths to a command


Media manipulation

Resize all .JPG wider than 1280px
Change an image density
Histogram matching
Make a timelapse from with all JPG in CWD
Extract a frame from a movie


git related

Get LOC in src/*.js for each contributor
List modified and staged files
List modified and unstaged files
List modified files since...
Reset working changes to latest origin
Update feature branch from master prior to PR


Basics

Repeat last command

!!
Repeat last argument


!$
alternatively, use ESC + .

Expand wildcards


CTRL + x, * will expand the last glob pattern:
$ rm *
# ctrl + x, *
$ rm fileA fileB fileC

Variable expansion


use double quotes to allow variable to expand (single quote won't interpolate anything):
$ echo '$(date +%Y-%m-%d_%H-%M)'
> $(date +%Y-%m-%d_%H-%M)

$ echo "$(date +%Y-%m-%d_%H-%M)"
> 2018-02-18_15-01

Array and list

mkdir {folderA,folderB,folderC}
touch file_{0..10}.txt
Loops

for c in {H,E,L,L,O}; do echo $c; done
for i in {1..10}; do echo $i; done
for f in *.png; do echo $f; done

use ${f%%.*} to print filename without extension:
for f in *.png; do echo ${f%%.*}; done

Sequential vs parallel loop execution

ecco () { sleep 1; echo $1; }

# sequential
for i in {0..10}; do ecco $i; done

# parallel
for i in {0..10}; do ecco $i & done; wait


File manipulation

Append timestamp

touch $(date +%Y-%m-%d_%H-%M).log
Lowercase a batch of files

for f in *; do mv "$f" "$f.tmp"; mv "$f.tmp" "`echo $f | tr "[:upper:]" "[:lower:]"`"; done
Batch change file extension in any depth

for f in {,**/}*.txt; do mv $f "${f/%.txt/.fr.txt}"; done
Delete files under 1kB

# Running dry
find * -type f -size -1024c -exec echo '{}' \;
# Actually deleting files
find * -type f -size -1024c -exec rm '{}' \;
^{See --size in find(1)}
Clean up SVGs and convert to php file


using svgo:
for f in *.svg; do svgo --input $f --pretty --enable={removeStyleElement,removeXMLNS,cleanupIDs}; mv $f ${f%%.*}.php; done

Pipe a list of paths to a command

cat files.txt | xargs $@ <COMMAND>


Media manipulation

Resize all .JPG wider than 1280px


using imagemagick/mogrify:
mogrify -quality 85 -resize '1280>' *.JPG

Change an image density


using imagemagick/density:
convert -units PixelsPerInch image-in-72-dpi.png -density 300 image-in-300-dpi.png

Histogram matching


using histmatch:
for i in {8143..8370}; do histmatch -c gray DSCF8142.JPG DSCF$i.JPG norm/$i.JPG; done

Make a timelapse from with all JPG in CWD


using ffmpeg:
ffmpeg -r 25 -pattern_type glob -i '*.JPG' -s hd1080 -vcodec libx264 timelapse.mp4

Extract a frame from a movie


using ffmpeg:
ffmpeg -i video.mp4 -ss 00:00:01.000 -vframes 1 cover.png


git related

Get LOC in src/*.js for each contributor

git ls-tree -r -z --name-only HEAD -- src/*.js | xargs -0 -n1 git blame --line-porcelain HEAD |grep  "^author "|sort|uniq -c|sort -nr
List modified and staged files

git diff --name-only --relative

use | xargs $@ <COMMAND> to run a command against this list:
git diff --name-only --relative | xargs $@ open

List modified and unstaged files

git ls-files -m --others --exclude-standard

use | xargs $@ <COMMAND> to run a command against this list:
git ls-files -m --others --exclude-standard | xargs $@ open

List modified files since...

# ... last commit
git diff --name-only HEAD HEAD~1 | cat

# ... latest release
git diff --name-only HEAD $(git describe --abbrev=0 --tags) | cat

# ... previous release
git diff --name-only HEAD $(git describe --abbrev=0 --tags `git rev-list --tags --skip=1 --max-count=1`) | cat
Reset working changes to latest origin


using current_branch from oh-my-zsh:

git reset --hard origin/$(current_branch)
Update feature branch from master prior to PR

git checkout feature
git fetch origin
git rebase origin/master