Bash String Manipulate
=====
String Length
Syntx:
${#variable_naem}
expr length "$string"
expr "$string" : '.*'
Example:
full_name="Matrix Zou"
$ echo "${#full_name}"
10
$ echo $(expr length "${full_name}")
10
$ echo $(expr "${full_name}" : '.*')
10
Length of Matching SubString from Beginning of String
Syntax:
expr match "$string" '$substring'
expr "$string" : '$substring'
Example:
$ full_name="Matrix Zou"
$ name="M.*x"
$ echo $(expr match "$full_name" $name)
6
$ echo $(expr match "$full_name" 'M.*x')
6
$ echo $(expr "$full_name" : '.*')
10
Index
Syntax:
expr index "$string" $substring
Example:
$ full_name="Matrix Zou"
$ name="M.*x"
$ echo $(expr index "$full_name" "$name")
1
$ echo $(expr index "$full_name" 'M.*x')
1
SubString Extraction
Syntax:
${string:position}
${string:position:length}
expr substr $string $position $length
NOTE: for expr substr, $position counted from 1
Example:
$ echo ${full_name:3}
rix Zou
$ echo ${full_name:3:3}
rix
$ echo $(expr substr "${full_name}" 4 3)
rix
$ echo ${full_name: -3}
Zou
$ echo ${full_name:(-3)}
Zou
$ index_of_substring=$(echo $(expr index "${full_name}" 'rix'))
$ echo ${full_name:$((--index_of_substring))}
rix Zou
Note: When using a negative offset, you need to separate the negative number from the colon by ` (space or ()`(brackets)
Substring Removal
From the beginning
Remove the described pattern trying to match it from the beginning of the string. The operator # will try to remove the shortest text matching the pattern, while ## tries to do it with the longest text matching.
Syntax:
${string#substring}
${string##substring}
Example:
$ name='Matrix Zou Matrix Zou'
$ echo "${name#M*Z}"
ou Matrix Zou
$ echo "${name##M*Z}"
ou
From the end
Syntax:
${string%substring}
${string%%substring}
Example:
$ echo "${name%Z*u}"
Matrix Zou Matrix
$ echo "${name%%Z*u}"
Matrix
Search and Replace
Substitute (replace) a substring matched by a pattern, on expansion time. The matched substring will be entirely removed and the given string will be inserted.
The First Occurrence
Syntax:
${string/substring/replacement}
Example:
$ name='Matrix Zou Matrix Zou'
$ echo "${name/Matrix/Test}"
Test Zou Matrix Zou
All Occurrence
Syntax:
${string//substring/replacement}
Example:
$ echo "${name//Matrix/Tetst}"
Test Zou Test Zou
Archoring, # from beginning, % from end
Syntax:
${string/#substring/replacement}
${string/%substring/replacement}
Example:
$ echo "${name/#Matrix/Test}"
Test Zou Matrix Zou
$ echo "${name/%Zou/Test}"
Matrix Zou Matrix Test
Remove Substring
Syntax:
${string/substring/}
${string/%substring/}
Example:
$ echo "${name/Matrix/}"
Zou Matrix Zou
$ echo "${name/Matrix}"
Zou Matrix Zou
$ echo "${name/%Zou/}"
Matrix Zou Matrix
$ echo "${name/%Zou}"
Matrix Zou Matrix
Substring Expansion
$ name="Matrix"
$ echo ${name:0:2} #=> "Ma" (slicing)
Ma
$ echo ${name::2} #=> "Ma" (slicing)
Ma
$ echo ${name::-1} #=> "Matri" (slicing)
Matri
$ echo ${name:(-1)} #=> "x" (slicing from end)
x
$ echo "${name: -1:1}" #=> same as above
x
$ echo ${name:(-2):1} #=> "x" (slicing from right)
i
$ echo "${name:1: -1}" #=> "atri" (negative length means slicing LENGTH charater(s) from end)
atri
Case Modification
^ modifies the first character to uppercase.
, modifies the first character to lowercase.
~ reverse the case for the first character.
When using the double-form (^^ / ,, / ~~ ), all characters are converted.
$ name="matrix"
$ echo ${name^}
Matrix
$ echo ${name~}
Matrix
$ echo ${name^^}
MATRIX
$ echo ${name~~}
MATRIX
$ name="MATrix"
$ echo ${name,}
mATrix
$ echo ${name~}
mATrix
$ echo ${name,,}
matrix
$ echo ${name~~}
matRIX
${parameter^pattern} / ${parameter^^pattern} / ${parameter,pattern} / ${parameter,,pattern}
While trying to convert case, it will compare with pattern. The pattern should not attempt to match more than one character.
$ name="matrix"
$ echo ${name^a}
matrix
$ echo ${name^m}
Matrix