#!/bin/bash
# array-strops.sh: String operations on arrays.

# Script by Michael Zick.
# Used in ABS Guide with permission.
# Fixups: 05 May 08, 04 Aug 08.

#  In general, any string operation using the ${name ... } notation
#+ can be applied to all string elements in an array,
#+ with the ${name[@] ... } or ${name[*] ...} notation.


arrayZ=( one two three four five five )

echo

# Trailing Substring Extraction
echo ${arrayZ[@]:0}     # one two three four five five
#                ^        All elements.

echo ${arrayZ[@]:1}     # two three four five five
#                ^        All elements following element[0].

echo ${arrayZ[@]:1:2}   # two three
#                  ^      Only the two elements after element[0].

echo "---------"


# Substring Removal

# Removes shortest match from front of string(s).

echo ${arrayZ[@]#f*r}   # one two three five five
#               ^       # Applied to all elements of the array.
                        # Matches "four" and removes it.

# Longest match from front of string(s)
echo ${arrayZ[@]##t*e}  # one two four five five
#               ^^      # Applied to all elements of the array.
                        # Matches "three" and removes it.

# Shortest match from back of string(s)
echo ${arrayZ[@]%h*e}   # one two t four five five
#               ^       # Applied to all elements of the array.
                        # Matches "hree" and removes it.

# Longest match from back of string(s)
echo ${arrayZ[@]%%t*e}  # one two four five five
#               ^^      # Applied to all elements of the array.
                        # Matches "three" and removes it.

echo "----------------------"


# Substring Replacement

# Replace first occurrence of substring with replacement.
echo ${arrayZ[@]/fiv/XYZ}   # one two three four XYZe XYZe
#               ^           # Applied to all elements of the array.

# Replace all occurrences of substring.
echo ${arrayZ[@]//iv/YY}    # one two three four fYYe fYYe
                            # Applied to all elements of the array.

# Delete all occurrences of substring.
# Not specifing a replacement defaults to 'delete' ...
echo ${arrayZ[@]//fi/}      # one two three four ve ve
#               ^^          # Applied to all elements of the array.

# Replace front-end occurrences of substring.
echo ${arrayZ[@]/#fi/XY}    # one two three four XYve XYve
#                ^          # Applied to all elements of the array.

# Replace back-end occurrences of substring.
echo ${arrayZ[@]/%ve/ZZ}    # one two three four fiZZ fiZZ
#                ^          # Applied to all elements of the array.

echo ${arrayZ[@]/%o/XX}     # one twXX three four five five
#                ^          # Why?

echo "-----------------------------"


replacement() {
    echo -n "!!!"
}

echo ${arrayZ[@]/%e/$(replacement)}
#                ^  ^^^^^^^^^^^^^^
# on!!! two thre!!! four fiv!!! fiv!!!
# The stdout of replacement() is the replacement string.
# Q.E.D: The replacement action is, in effect, an 'assignment.'

echo "------------------------------------"

#  Accessing the "for-each":
echo ${arrayZ[@]//*/$(replacement optional_arguments)}
#                ^^ ^^^^^^^^^^^^^
# !!! !!! !!! !!! !!! !!!

#  Now, if Bash would only pass the matched string
#+ to the function being called . . .

echo

exit 0

#  Before reaching for a Big Hammer -- Perl, Python, or all the rest --
#  recall:
#    $( ... ) is command substitution.
#    A function runs as a sub-process.
#    A function writes its output (if echo-ed) to stdout.
#    Assignment, in conjunction with "echo" and command substitution,
#+   can read a function's stdout.
#    The name[@] notation specifies (the equivalent of) a "for-each"
#+   operation.
#  Bash is more powerful than you think!