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Strings,

• Index
• Substring Extraction
• Substring Removal
• Substring Replacement

 

Index

expr index $string $substring
Numerical position in $string of first character in $substring that matches.

stringZ=abcABC123ABCabc
echo `expr index "$stringZ" C12`             # 6
                                             # C position.

echo `expr index "$stringZ" 1c`              # 3
# 'c' (in #3 position) matches before '1'.

Substring Extraction

${string:position}
Extracts substring from $string at $position.
If the $string parameter is "*" or "@", then this extracts the positional parameters, [1] starting at $position.

${string:position:length}
Extracts $length characters of substring from $string at $position.

stringZ=abcABC123ABCabc
#       0123456789.....

echo ${stringZ:0}                            # abcABC123ABCabc
echo ${stringZ:1}                            # bcABC123ABCabc
echo ${stringZ:7}                            # 23ABCabc

echo ${stringZ:7:3}                          # 23A
                                             # Three characters of substring.


# Is it possible to index from the right end of the string?
    
echo ${stringZ:-4}                           # abcABC123ABCabc
# Defaults to full string, as in ${parameter:-default}.
# However . . .

echo ${stringZ:(-4)}                         # Cabc 
echo ${stringZ: -4}                          # Cabc

expr substr $string $position $length
Extracts $length characters from $string starting at $position.

stringZ=abcABC123ABCabc
#       123456789......
#       1-based indexing.

echo `expr substr $stringZ 1 2`              # ab
echo `expr substr $stringZ 4 3`              # ABC

expr match "$string" '\($substring\)'
Extracts $substring at beginning of $string, where $substring is a regular expression.

stringZ=abcABC123ABCabc

echo `expr match "$stringZ" '\(.[b-c]*[A-Z]..[0-9]\)'`   # abcABC1
echo `expr "$stringZ" : '\(.[b-c]*[A-Z]..[0-9]\)'`       # abcABC1
echo `expr "$stringZ" : '\(.......\)'`                   # abcABC1
# All of the above forms give an identical result.

expr "$string" : '.*\($substring\)'
Extracts $substring at end of $string, where $substring is a regular expression.

stringZ=abcABC123ABCabc

echo `expr match "$stringZ" '.*\([A-C][A-C][A-C][a-c]*\)'`    # ABCabc
echo `expr "$stringZ" : '.*\(......\)'`                       # ABCabc

Substring Removal

${string#substring}
Strips shortest match of $substring from front of $string.

${string##substring}
Strips longest match of $substring from front of $string.

stringZ=abcABC123ABCabc

echo ${stringZ#a*C}      # 123ABCabc
# Strip out shortest match between 'a' and 'C'.

echo ${stringZ##a*C}     # abc
# Strip out longest match between 'a' and 'C'.

${string%substring}
Strips shortest match of $substring from back of $string.

${string%%substring}
Strips longest match of $substring from back of $string.

stringZ=abcABC123ABCabc

echo ${stringZ%b*c}      # abcABC123ABCa
# Strip out shortest match between 'b' and 'c', from back of $stringZ.

echo ${stringZ%%b*c}     # a
# Strip out longest match between 'b' and 'c', from back of $stringZ.

Substring Replacement

${string/substring/replacement}
Replace first match of $substring with $replacement.

${string//substring/replacement}
Replace all matches of $substring with $replacement.

stringZ=abcABC123ABCabc

echo ${stringZ/abc/xyz}           # xyzABC123ABCabc
                                  # Replaces first match of 'abc' with 'xyz'.

echo ${stringZ//abc/xyz}          # xyzABC123ABCxyz
                                  # Replaces all matches of 'abc' with # 'xyz'.

${string/#substring/replacement}
If $substring matches front end of $string, substitute $replacement for $substring.

${string/%substring/replacement}
If $substring matches back end of $string, substitute $replacement for $substring.

stringZ=abcABC123ABCabc

echo ${stringZ/#abc/XYZ}          # XYZABC123ABCabc
                                  # Replaces front-end match of 'abc' with 'XYZ'.

echo ${stringZ/%abc/XYZ}          # abcABC123ABCXYZ
                                  # Replaces back-end match of 'abc' with 'XYZ'.

 

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