Bash-Beginners-Guide

Bash Guide for Beginners
9.5.3. Examples
In the following example, file names are converted to lower case. If no conversion needs to be done, a
continue statement restarts execution of the loop. These commands don't eat much system resources, and
most likely, similar problems can be solved using sed and awk. However, it is useful to know about this kind
of construction when executing heavy jobs, that might not even be necessary when tests are inserted at the
correct locations in a script, sparing system resources.
[carol@octarine ~/test] cat tolower.sh
#!/bin/bash
# This script converts all file names containing upper case characters into file# names containin
LIST="$(ls)"
for name in "$LIST"; do
if [[ "$name" != *[[:upper:]]* ]]; then
continue
fi
ORIG="$name"
NEW=`echo $name | tr 'A-Z' 'a-z'`
mv "$ORIG" "$NEW"
echo "new name for $ORIG is $NEW"
done
This script has at least one disadvantage: it overwrites existing files. The noclobber option to Bash is only
useful when redirection occurs. The -b option to the mv command provides more security, but is only safe in
case of one accidental overwrite, as is demonstrated in this test:
[carol@octarine ~/test] rm *
[carol@octarine ~/test] touch test Test TEST
[carol@octarine ~/test] bash -x tolower.sh
++ ls
+ LIST=test
Test
TEST
+ [[ test != *[[:upper:]]* ]]
+ continue
+ [[ Test != *[[:upper:]]* ]]
+ ORIG=Test
++ echo Test
++ tr A-Z a-z
+ NEW=test
+ mv -b Test test
+ echo 'new name for Test is test'
new name for Test is test
+ [[ TEST != *[[:upper:]]* ]]
+ ORIG=TEST
++ echo TEST
++ tr A-Z a-z
+ NEW=test
+ mv -b TEST test
+ echo 'new name for TEST is test'
new name for TEST is test
Chapter 9. Repetitive tasks 116