Bash can be used to perform some basic string manipulation. It is best to put these to use when the logic does not get overly complicated. In this post we will look at some useful and commmonly used string manipulation technques that should come in handy in our every day scripting tasks.
- Concatinate strings
- Delimit string with character
- Delimit string with character and convert it into an array
- Get Length of string
- Get substring from a specific position
- Get substring from a given start position to a given end position
- Replace one substring with another, in a string
- Delete substring from a string
- Remove all occurences of a substring in a string
- Remove substring only if its a prefix to string
- Remove substring only if its a suffix to string
- Check if substring exists in string
- Convert string to uppercase
- Convert string to lowercase
- Convert the first character to upperase
- Convert the first character to lowercase
- Convert only certain characters to uppercase
- Convert only certain characters to lowercase
String manipulation with Bash
Concatinate strings
Concatinate two strings variables x and y.
$ x="Unix" $ y="Utils" $ echo $x$y
UnixUtils
Delimit string with character
Delimit string with character and convert them into separate variables.
$ x='Unix-Utils-World' $ IFS=- read -r x y z <<< "$x" $ echo $x
Unix
$ echo $y
Utils
$ echo $z
World
Delimit string with character and convert it into an array
$ x='Unix-Utils-World'
$ IFS=- read -ra string <<< "$x"
$ echo ${string[@]}
Unix Utils World
$ echo ${string[0]}
Unix
$ echo ${string[1]}
Utils
$ echo ${string[2]}
World
Get Length of string
$ name=unixutils
$ echo ${#name}
9
Get substring from a specific position
$ name=unixutils
$ echo ${name:0}
unixutils
$ echo ${name:1}
nixutils
$ echo ${name:3}
xutils
$ echo ${name:4}
utils
Get substring from a given start position to a given end position
$ name=unixutils $ echo $name
unixutils
$ echo ${name:0:4}
unix
$ echo ${name:0:7}
unixuti
Note that, with the above example one can get the first 2 characters from string by setting the start and end positions as 0 to 2, respectively.
$ str="unixutils"
$ echo ${str:0:2}
un
For example, to get the last two characters, it can be done by the following method that uses negative numbers for positional arguement.
$ str="unixutils"
$ echo ${str:(-2)}
ls
Replace one substring with another, in a string
$ x='Unix-Utils-World'
$ echo ${x/World/website}
Unix Utils website
$ echo ${x/World/'website welcomes you!'}
Unix Utils website welcomes you!
Delete substring from string
$ str='Unix-Utils-World' $ echo $str
Unix-Utils-World
$ echo ${str/-World}
Unix-Utils
Remove all occurences of a substring in a string
In the below two examples, the first one removes only the first occurence of the substring, but the second examples removes all occurences of a substring.
$ str="unix-utils-world"
$ echo ${str/-}
unixutils-world
$ echo ${str//-}
unixutilsworld
Remove substring only if its a prefix to string
$ str="-unix-utils-world-"
$ echo ${str/#-}
unix-utils-world-
Remove substring only if its a suffix to string
$ str="-unix-utils-world-"
$ echo ${str/%-}
-unix-utils-world
Check if substring exists in string
string='UnixUtils welcomes you' if [[ $string = *"welcomes you"* ]]; then echo "substring found!" fi
substring found!
Convert string to uppercase
$ str="unixutils" $ echo $str
unixutils
$ echo ${str^^}
UNIXUTILS
Convert string to lowercase
$ str="UnixUTILS" $ echo $str
UnixUTILS
$ echo ${str,,}
unixutils
Convert the first character to upperase
$ string="unixutils"
$ echo ${string^}
Unixutils
Convert the first character to lowercase
$ string="Unixutils"
$ echo ${string,}
unixutils
Convert only certain characters to uppercase
$ string="unixutils"
$ echo ${string^^[u]}
UnixUtils
$ echo ${string^^[ui]}
UnIxUtIls
Convert only certain characters to lowercase
$ string="UNIXUTILS"
$ echo ${string,,[U]}
uNIXuTILS
$ echo ${string,,[US]}
uNIXuTILs
Bash can be used to manipulate strings when the requirements are simple. However when things get complicated, such as to work on complex patterns and logic, bash does not fair well. In such cases very sophisticated and commonly used data manipulation ‘awk’ is prefered.
