Converting CamelCase to lowerCamelCase with POSIX Shell

Question

I am trying to only change the first letter of a string to lowercase using a Shell script. Ideally a simple way to go from CamelCase to lowerCamelCase.

GOAL:

$DIR="SomeString"
# missing step
$echo $DIR
someString

I have found some great resources for doing this to the entire string but not just altering the first letter and leaving the remaining string untouched.

Answer 1

If your shell is recent enough, you can use the following parameter expansion:

DIR="SomeString"   # Note the missing dollar sign.
echo ${DIR,}

Answer 2

Alternative solution (will work on old bash too)

DIR="SomeString"
echo $(echo ${DIR:0:1} | tr "[A-Z]" "[a-z]")${DIR:1}

prints

someString

for assing to variable

DIR2="$(echo ${DIR:0:1} | tr "[A-Z]" "[a-z]")${DIR:1}"
echo $DIR2

prints

someString

alternative perl

DIR3=$(echo SomeString | perl -ple 's/(.)/\l$1/')
DIR3=$(echo SomeString | perl -nle 'print lcfirst')
DIR3=$(echo "$DIR"     | perl -ple 's/.*/lcfirst/e'

some terrible solutions;

DIR4=$(echo "$DIR" | sed 's/^\(.\).*/\1/' | tr "[A-Z]" "[a-z]")$(echo "$DIR" | sed 's/^.//')
DIR5=$(echo "$DIR" | cut -c1 | tr '[[:upper:]]' '[[:lower:]]')$(echo "$DIR" | cut -c2-)

All the above is tested with OSX's /bin/bash.