Bash

bash: Simple way to get n-th column

 in Bash / GNU/Linux  tagged column / cut / delimiter by

Using cut you can select any column and define a custom delimiter to support multiple input formats you can select a column (or more) with barely minimum code.

cut -d',' -f2 myFile.csv

The above command will read the file myFile.csv (which is a CSV file) break it down to columns using the ‘,‘ character and then get the second column.

The option -f specifies which field (column) you want to extract, and the option -d specifies what is the field delimiter (column) that is used in the input file.

The -f parameter allows you to select multiple columns at the same time. You can achieve that by defining multiple columns separated using the ‘,‘ and by defining ranges using the - character.

Examples

  • -f1 selects the first column
  • -f1,3,4 selects columns 1, 3 and 4
  • -f1-4 selects all columns in the range 1-4
  • -f1,3,5-7,9 selects columns 1,3,8 and all the columns in the range 5-7

ffmpeg: Extract audio from .MKV to .MP3 13

 in Bash / GNU/Linux  tagged audio / extract / ffmpeg / mkv / mp3 / video by

The following command will find all mkv files that are in the current directory and in all sub-folders and extract the audio to mp3 format.

find . -type f -name "*.mkv" -exec bash -c 'FILE="$1"; ffmpeg -i "${FILE}" -vn -c:a libmp3lame -y "${FILE%.mkv}.mp3";' _ '{}' \;

The filename of the audio file will be the same as the mkv video with the correct extension. The mkv extension will be removed and replaced by the mp3 extension e.g hi.mkv will create a new file named hi.mp3

Git: Delete all local branches

 in Bash  tagged delete / fetch / git / grep / local branch / merged / prune / xargs by

The following command will:

  • print all branches that were merged to master
  • then filter out the branch named master and the branch you are currently switched to
  • and finally, it will delete the rest (one branch at a time).
git branch --merged master | grep -v -e "\*" -e "master" | xargs git branch -D

Tip:

To cleanup any remote-tracking references that no longer exist on the remote use the following:

git fetch --prune

Bash/FFMPEG: Batch resize .mp4 videos to fixed resolution 2

 in Bash / GNU/Linux  tagged bash / ffmpeg / mp4 / resize by

We needed to shrink a bunch of mp4 videos so that they would have the same size as the screen of an android device.
We did that both to save space on the internal memory of the device and to make the device perform as efficient as possible as it would not have to shrink the video on the fly.

The command we used was the following:

find . -type f -name "*.mp4" -exec bash -c 'FILE="$1"; ffmpeg -i "${FILE}" -s 1280x720 -acodec copy -y "${FILE%.mp4}.shrink.mp4";' _ '{}' \;

What this command does is the following:

  • Find all files in current folder (and sub-folders) that have the extension .mp4
  • For each file, create a new bash instance in which it will call ffmpeg taking as first parameter the filename that matched
  • -i "${FILE}" – ffmpeg will take as input the filename we matched
  • -s 1280x720 – Then change the video size to 1280x720
  • -acodec copy – It will keep the audio as is
  • -y "${FILE%.mp4}.shrink.mp4 – Finally, create a new file (or overwrite existing) that has the extension .shrink.mp4 in the same folder