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Bash Scripting

Filenames

Filenames and directory names are merely strings, and we do a lot coding that has to work with them. Here are 2 of the most common and useful commands.

• basename
  extract the filename of a complete pathname
• dirname
  extract from the final slash forward

basename

mediaPath="/Volumes/echo1/Media backup/Plex/Documentaries/Arctic Live [1of3] (2016)/Arctic Live [1of3] (2016).mp4"
basename "$mediaPath"
echo "Assign to a variable ..."
fileMedia=$(basename "$mediaPath")
echo "\$fileMedia: $fileMedia"

gives me

dirname

The companion to basename. It works with absolute and relative pathnames.

pwd
dirPath="/Volumes/echo1/Media backup/Plex/Documentaries/Arctic Live [1of3] (2016)/Arctic Live [1of3] (2016).mp4"
echo "\$dirPath: -->$dirPath<--"
echo "Assign to a variable ..."
dirVar=$(dirname "$dirPath")
echo "\$dirVar: -->$dirVar<--"
echo "Now cd to that directory ..."
cd "$dirVar"
pwd
dirName=$(dirname "$dirVar")
echo "\$dirName: -->$dirName<--"

This results in

Practice using these 2 commands - they will become familiar and more useful.

Sometimes we want to know details about a file that isn't readily available, but we would like to use it somehow in a script. Since we are mostly dealing with text (ASCII) files in scripting, what tools may be useful to us?

Here are a few that may find their way into your toolbox:

wc

This one is a native command-line tool used on text (ASCII) files - word count, and used like this:

• how many 'words' in this file
  wc -w kb.sql
  69922
• how many lines in this file
  wc -l kb.sql
  3079
• how many characters in this file
  wc -m kb.sql
  601819
• how many bytes in this file
  wc -c kb.sql
  601919

See SS64 for specifics.

Now you can get this information and put it into a bash variable, right?

file

Another native CLI application, tells us the file format of a file.

• file upsert.svg
  upsert.svg: SVG Scalable Vector Graphics image
• file colors1.jpg
  colors1.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 144x144, segment length 16, Exif Standard: [TIFF image data, big-endian, direntries=4, xresolution=62, yresolution=70, resolutionunit=2], baseline, precision 8, 1330x1208, components 3
• file expanse.html
  expanse.html: HTML document text, Unicode text, UTF-8 text
• file bash.json
  bash.json: JSON data
• file bash.css
  bash.css: ASCII text
• file "Carl Hiaasen - Razor Girl.mobi"
  Carl Hiaasen - Razor Girl.mobi: Mobipocket E-book "Razor Girl", 824701 bytes uncompressed, version 6, codepage 65001
• file "S01E01 Beyond The Now.mkv"
  S01E01 Beyond The Now.mkv: Matroska data
• file S01E01.avi
  RIFF (little-endian) data, AVI, 640 x 360, 25.00 fps, video: XviD, audio: MPEG-1 Layer 3 (stereo, 48000 Hz)

As you can see, all types of files (binary as well as text) have information that can be useful - if you can get at it. These tools may be just what you need.

3rd Party Tools

We've discussed the use of ExifTool several times as an excellent non-native tool that can be used in bash (or any) scripting to pull metadata (ID3) tags from several digital cameras, as well as several audio and video file types.

If the task you are trying to do doesn't seem to have anything available natively, don't be afraid to look elsewhere, preferably at reliable sources.