help.md

Command Line Tips

delete all files named 'rc.conf':

find . -name "rc.conf" -exec rm '{}' \;

delete all empty directories:

find . -empty -exec rmdir '{}' \;

run a command on all of the regular files:

find . -type f -exec clean '{}' \;

7z with password:

7z u -p{password} -mhe target.7z files

git undo commit

git reset --soft HEAD\^

git revert all changes

git checkout -f
or
git reset --HARD

git point master to origin/master

git reset --hard origin/master

git show specific version of file

git show {branch/tag/commit}:{path/to/file/from/repo/root}   

example:
  git show master:dir1/dir2/file.txt

git show orphaned commites

git reflog --all
git fsck --lost-found

git abort merge/cherry-pick

git reset --merge

git remove file from repo history

git filter-branch \ 
  --index-filter 'git rm --cached --ignore-unmatch path/to/file' \
  {from}..{to}

git delete branch

git branch -d {branch}
git push --delete origin {branch}

git remove untracked files

git clean -f            (all untracked files)
git clean -f -n         (dry run)
git clean -f -n {path}  (dry run on files in path)

ImageMagick resize

convert --sample 50% input.png output.jpg

ImageMagick convert to 2 colors (2bit, 2-bit)

convert -colors 2 input.png output.png

ImageMagick create pdf

convert file1.png file2.png output.pdf
convert -page {width}x{height} file1.png file2.png output.pdf

ImageMagick flip images

convert arrow-left.png -flop arrow-right.gif
convert arrow-up.png   -flip arrow-down.gif

reset terminal

ctrl+c reset
ctrl+c stty sane

diff directories

# show only summary (e.g. "file1 differs"):
diff -rq dirA dirB

# show diff for each file:
diff -r dirA dirB

awk - get second column

awk '{ print $2 }' 

awk - sum values of 6th column:

awk '{s+=$6} END { print s }'

awk - format number with thousand commas (1,000,000)

awk '{ printf "%''d\n", $1 }' 
awk "{ printf \"%'d\n\", $1 }" 

count number of lines

wc -l

zsh remove extension

name='file.ext'
echo ${name:r} # => outputs 'file'

zsh basename

fullpath='/path/to/file.ext'
echo ${fullpath:t} # => outputs 'file.ext'

zsh regexp

name='file-bob.txt'
echo ${name:s/bob/joe} # => outputs 'file-joe.txt'

zsh rebuild (reindex) autocomplete

compinit

tmux - detach all other clients

tmux attach -d
tmux attach -d -t specific_session_name

bzr - pull repository

bzr branch bzr+ssh://{username}@{hostname}/path/to/repo local_dir_to_create

irc - register nick

/msg nickserv help
/msg nickserv register <password> <email-address>

Fix "There is no connected camera" macbook air problem

sudo killall VDCAssistant
(see https://discussions.apple.com/thread/4158054?start=0&tstart=0)

format xml

cat file.xml | xmllint --format -

hex view

od -xcb {file}

mac - clear dns cache

dscacheutil -flushcache

bash - read file line by line

cat $filename | while read line; do echo $line; done

psql show all tables

psql -h {host} -p {port} -U {username} {database} ? - show help (all commands) \l - show all databases \d - show all tables and other objects \dt - show all tables \db - show all tablespaces \d+ - describe table

cut prefix

echo "hello" | cut -c 3- # will output "llo"