Advanced Bash−Scripting Guide

echo '${var1#$pattern1} =' "${var1#$pattern1}" # d12345abc6789
# Shortest possible match, strips out first 3 characters abcd12345abc6789
# ^^^^^ |−|
echo '${var1##$pattern1} =' "${var1##$pattern1}" # 6789
# Longest possible match, strips out first 12 characters abcd12345abc6789
# ^^^^^ |−−−−−−−−−−|
echo; echo
pattern2=b*9
# everything between 'b' and '9'
echo "var1 = $var1" # Still abcd12345abc6789
echo "pattern2 = $pattern2"
echo
echo '${var1%pattern2} =' "${var1%$pattern2}" # abcd12345a
# Shortest possible match, strips out last 6 characters abcd12345abc6789
# ^^^^ |−−−−|
echo '${var1%%pattern2} =' "${var1%%$pattern2}" # a
# Longest possible match, strips out last 12 characters abcd12345abc6789
# ^^^^ |−−−−−−−−−−−−−|
# Remember, # and ## work from the left end of string,
# % and %% work from the right end.
echo
exit 0
Advanced Bash−Scripting Guide
Example 9−17. Renaming file extensions:
#!/bin/bash
# rfe
# −−−
# Renaming file extensions.
#
# rfe old_extension new_extension
#
# Example:
# To rename all *.gif files in working directory to *.jpg,
# rfe gif jpg
ARGS=2
E_BADARGS=65
if [ $# −ne "$ARGS" ]
then
echo "Usage: `basename $0` old_file_suffix new_file_suffix"
exit $E_BADARGS
fi
for filename in *.$1
# Traverse list of files ending with 1st argument.
do
mv $filename ${filename%$1}$2
# Strip off part of filename matching 1st argument,
#+ then append 2nd argument.
done
Chapter 9. Variables Revisited 89