Converting CamelCase to lowerCamelCase with POSIX Shell - bash

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.

Answer 3

With sed:
var="SomeString"
echo $var | sed 's/^./\L&/'
^ means the start of the line
\L is the command to make the match in lowercase
& is the whole match

Answer 4

Perl solution:
DIR=SomeString
perl -le 'print lcfirst shift' "$DIR"

Answer 5

Since awk hasn't yet been mentioned, here's another way you could do it (requires GNU awk):
dir="SomeString"
new_dir=$(awk 'BEGIN{FS=OFS=""}{$1=tolower($1)}1' <<<"$dir")
This sets the input and output field separators to an empty string, so each character is a field. The tolower function does what you think it does. 1 at the end prints the line. If your shell doesn't support <<< you can do echo "$dir" | awk ... instead.

Answer 6

If you are looking for a POSIX compliant solution then have a look at typeset.
var='SomeString'
typeset -lL1 b="$var"
echo "${b}${var#?}"
Output:
someString
The typeset command creates a special variable that is lowercase, left aligned and one char long. ${var#?} trims the first occurrence of pattern from the start of $var and ? matches a single
character.