Removing Substring In Bash With Parameter Expansion

The aim of this page📝is to see how a part of the string can be removed using the parameter expansion feature of bash.

• parameter expansion allows quite powerful string manipulation in bash
• e.g. the length of a variable is obtained via

${#<var>}

• there are 3 elements to parameter expansion syntax
• ${} const wrapper
• <var> variable name
• #,... special character defining the type of expansion

1. syntax

SYNTAX              | LENGTH   | FROM
--------------------|----------|--------------
${<var>#<pattern>}  | shortest | the beginning
${<var>##<pattern>} | longest  | the beginning
${<var>%<pattern>}  | shortest | the end
${<var>%%<pattern>} | longest  | the end

• <patterns> are globbing patterns using
• * match any string
• ? match single char
• [] match set of chars

2. example

i="/users/pkutaj/demo.txt"

<!-- SHORTEST FROM THE BEGINNING -->
>>> echo ${i#*/}
users/pkutaj/demo.txt

<!-- LONGEST FROM THE BEGINNING-->
>>> echo ${i##*/}
demo.txt

<!-- SHORTEST FROM THE END -->
>>> echo ${i%/*}
/users/pkutaj

<!-- LONGEST FROM THE END -->
>>> echo ${i%/*}

🠉 all is removed

3. links

• Shell Parameter Expansion (Bash Reference Manual)