Parameter Part Two

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.

Removing Fixed Prefixes and Suffixes

Often in Linux you work with file paths and extensions:

Component	Example 1	Example 2	Example 3
Prefix	`/home/my_username/`	`/home/my_username/`	`/usr/bin/`
Name	`text_file`	`text_file2`	`app.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.

Using Wildcards for General Cases

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

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

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.

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

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

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

Choosing the Right Operator

Operator	Description	Example
`${var#…}`	Remove shortest prefix match	Strip up to first delimiter
`${var##…}`	Remove longest prefix match	Strip up to last delimiter
`${var%…}`	Remove shortest suffix match	Remove first occurrence from end
`${var%%…}`	Remove longest suffix match	Remove 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.

Introduction

Conventions

Refresher

Streams

Expansions - Part One

Globs

Expansions - Part Two

Special Shell Variables

Arrays

Good Practices applied

awk

sed

Parameter Part Two

Removing Fixed Prefixes and Suffixes

Using Wildcards for General Cases

Strip the First Word

Strip the Last Word

Handling Unix‐Style Filenames

Remove All Directory Components

Strip File Extension

Choosing the Right Operator

Links and References

Watch Video

Practice Lab

​Removing Fixed Prefixes and Suffixes

​Using Wildcards for General Cases

​Strip the First Word

​Strip the Last Word

​Handling Unix‐Style Filenames

​Remove All Directory Components

​Strip File Extension

​Choosing the Right Operator

​Links and References

Watch Video

Practice Lab

Removing Fixed Prefixes and Suffixes

Using Wildcards for General Cases

Strip the First Word

Strip the Last Word

Handling Unix‐Style Filenames

Remove All Directory Components

Strip File Extension

Choosing the Right Operator

Links and References