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In Part One, we covered basic parameter‐expansion techniques for stripping fixed prefixes or suffixes. Here, we’ll explore more flexible patterns using wildcards to handle arbitrary extensions, path segments, or words in a string.

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Removing Fixed Prefixes and Suffixes

Often in Linux you work with file paths and extensions:
ComponentExample 1Example 2Example 3
Prefix/home/my_username//home/my_username//usr/bin/
Nametext_filetext_file2app.py
Suffix.txt.txt.py
A fixed‐suffix removal like ${var%.txt} only matches when the filename actually ends in .txt: 
$ var="/home/my_username/text_file.txt"
$ echo "${var%.txt}"
/home/my_username/text_file

$ var="/home/my_username/text_file2.txt"
$ echo "${var%.txt}"
/home/my_username/text_file2

$ var="/usr/bin/app.py"
$ echo "${var%.txt}"
/usr/bin/app.py
Using ${var%.txt} leaves .py files untouched. For arbitrary extensions or dynamic patterns, you’ll need wildcards.

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Using Wildcards for General Cases

By introducing * in the pattern, you can remove everything up to or after a delimiter (space, slash, dot, etc.).

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Strip the First Word

For a space-separated string, ${var#* } removes the shortest match from the front (everything up to the first space): 
export position1="Senior Cloud Architect"
export position2="Senior DevOps Engineer"
export position3="Associate Frontend Engineer"
export position4="Junior Software Developer"

echo "${position1#* }"   # Cloud Architect
echo "${position2#* }"   # DevOps Engineer
echo "${position3#* }"   # Frontend Engineer
echo "${position4#* }"   # Software Developer

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Strip the Last Word

Using ${var% *} removes the shortest match from the end (from the last space onward): 
echo "${position1% *}"   # Senior Cloud
echo "${position2% *}"   # Senior DevOps
echo "${position3% *}"   # Associate Frontend
echo "${position4% *}"   # Junior Software
Always pair * with a literal character (e.g., space or slash). A pattern like ${var%*} matches the entire string, returning an empty result.

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Handling Unix‐Style Filenames

Consider two variables: 
my_text_file="/home/my_username/text_file.txt"
my_python_file="/usr/bin/app.py"
  • Prefix: directory path
  • Name: file name
  • Suffix: extension

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Remove All Directory Components

  • ${var#*/} strips up to the first slash
  • ${var##*/} strips up to the last slash (longest‐prefix removal)
echo "${my_text_file#*/}"    # home/my_username/text_file.txt
echo "${my_python_file#*/}"  # usr/bin/app.py

echo "${my_text_file##*/}"   # text_file.txt
echo "${my_python_file##*/}" # app.py

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Strip File Extension

Use shortest‐suffix (%) or longest‐suffix (%%). With a single dot, both behave identically: 
echo "${my_text_file%.*}"   # /home/my_username/text_file
echo "${my_text_file%%.*}"  # /home/my_username/text_file

echo "${my_python_file%.*}"   # /usr/bin/app
echo "${my_python_file%%.*}"  # /usr/bin/app

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Choosing the Right Operator

OperatorDescriptionExample
${var#…}Remove shortest prefix matchStrip up to first delimiter
${var##…}Remove longest prefix matchStrip up to last delimiter
${var%…}Remove shortest suffix matchRemove first occurrence from end
${var%%…}Remove longest suffix matchRemove all occurrences from end
  • Use shortest‐suffix (%) for extensions.
  • Use longest‐prefix (##) for directory paths.
With these four operators, you can tailor string manipulations to filenames, paths, or any delimited data.

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