Bash string manipulation involves using parameter expansion to modify the value of a variable. Here are some common string manipulation techniques in bash:
Removing a substring from the front of a string
Remove shortest match of a pattern from the front
var="System Commands"
echo ${var#* }
This removes the shortest match of *
(anything followed by a space) from the beginning of the string, resulting in Commands
.
Remove longest match of a pattern from the front
var="System Commands are useful"
echo ${var##* }
This removes the longest match of *
from the beginning of the string, resulting in useful
.
Removing a substring from the end of a string
Remove shortest match of a pattern from the end
var="System Commands"
echo ${var% *}
This removes the shortest match of *
(space followed by anything) from the end of the string, resulting in System
.
Remove longest match of a pattern from the end
var="System Commands are useful"
echo ${var%% *}
This removes the longest match of *
from the end of the string, resulting in System
.
Extracting a substring
Extract substring from position
var="System Commands"
echo ${var:0:6}
This extracts 6 characters starting from position 0, resulting in System
.
Length of a string
var="System Commands"
echo ${#var}
This returns the length of the string, which is 15
.
Replacing part of a string
Replace first match
var="System Commands"
echo ${var/Commands/Operations}
This replaces the first occurrence of Commands
with Operations
, resulting in System Operations
.
Replace all matches
var="System Commands Commands"
echo ${var//Commands/Operations}
This replaces all occurrences of Commands
with Operations
, resulting in System Operations Operations
.
Example for extracting the first word using string manipulation
To extract the first word from a string, you can use:
var="System Commands"
echo ${var%% *}
This removes everything from the first space to the end of the string, effectively extracting the first word, resulting in System
.
These techniques allow you to manipulate strings in various ways directly within bash scripts, providing powerful tools for text processing without needing external utilities.
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