Concatenating Strings

Variables can be joined by placing them adjacent to each other.

prefix="sys"
suffix="_log"
combined="${prefix}${suffix}"
echo "$combined"  # Output: sys_log

Extracting Substrings by Index

Retrieve a portion of a string by specifying the starting position and length using the format ${variable:offset:length}.

text="deployment"
segment="${text:3:5}"
echo "$segment"  # Output: loyme

Extracting from the End

To capture characters counting backward from the string's end, use a negative offset. A space must precede the minus sign to avoid syntax errors.

identifier="server_42"
tail_part="${identifier: -2}"
echo "$tail_part"  # Output: 42

Removing Substrings Based on Patterns

Pattern matching allows removing text from the beginning or end of a string.

• ${variable#pattern}: Removes the shortest match from the start.
• ${variable##pattern}: Removes the longest match from the start.
• ${variable%pattern}: Removes the shortest match from the end.
• ${variable%%pattern}: Removes the longest match from the end.

path="/usr/local/bin/app.sh"
echo "${path#*/}"   # Output: usr/local/bin/app.sh
echo "${path##*/}"  # Output: app.sh

endpoint="api.v2.service.io"
echo "${endpoint%.*}"   # Output: api.v2.service
echo "${endpoint%%.*}"  # Output: api

Replacing Patterns

Substitute matched text with new values. Globbing meta-characters like * and ? are permitted in patterns.

• ${variable/pattern/replacement}: Replaces the first occurrence.
• ${variable//pattern/replacement}: Replaces all occurrences.
• ${variable/#pattern/replacement}: Replaces a match at the beginning.
• ${variable/%pattern/replacement}: Replaces a match at the end.

record="user:admin:role:admin"
echo "${record/admin/guest}"   # Output: user:guest:role:admin
echo "${record//admin/guest}"  # Output: user:guest:role:guest
echo "${record/#user/system}"  # Output: system:admin:role:admin
echo "${record/%admin/root}"   # Output: user:admin:role:root

Deleting Patterns

Omitting the replacement string deletes the matched text.

record="user:admin:role:admin"
echo "${record/admin}"    # Output: user::role:admin
echo "${record//admin}"   # Output: user::role:
echo "${record/#user}"    # Output: :admin:role:admin
echo "${record/%admin}"   # Output: user:admin:role:

Case Conversion

Switch the entire string between uppercase and lowercase.

• ${variable^^}: Converts all characters to uppercase.
• ${variable,,}: Converts all characters to lowercase.

val="config"
echo "${val^^}"  # Output: CONFIG

VAL="TEMPORARY"
echo "${VAL,,}"  # Output: temporary