String Processing with Bash

There are various tools built into bash that enable you to manipulate a variable or string which come in handy when writing shell scripts. Here are a few notable ones:

Find the length of a string

${#string}

Get a Substring from a String

${string:pos} or ${string:pos:len}

Removing Substrings from a String

${string#substr} ${string%substr} ${string##substr} ${string%%substr}

Some examples

Here’s a few examples of how you can process a variable that points to an absolute path of a file and shows how to extract certain parts of said file’s path:

var=/home/user/code/blogstuff/index.html.j2 echo ${var} # => /home/user/code/blogstuff/index.html.j2 echo ${var#*.} # => html.j2 echo ${var##*.} # => j2 echo ${var%/*.*} # => /home/user/code/blogstuff

Replace a Substring of a String

${string/pattern/substr} # => Replaces the 1st match found ${string//pattern/substr} # => Replaces all of the matches found

Replace the Beginning or End of a String

${string/#pattern/substr} ${string/%pattern/substr} file=${var##/*/} # => index.html.j2 echo ${file/#index/fubar} # => fubar.html.j2 echo ${file/%j2/fubar} # => index.html.fubar

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