tr(1)
tr [opt] str1 [str2]
-d delete characters in str1
-s squeeze repeating sequence of characters in str1
Examples
To lower
echo MoOsE | tr '[:upper:]' '[:lower:]'
# output: moose
Replace characters
echo moose | tr 'o' '-'
# output: m--se
echo moose | tr 'os' '-'
# output: m---e
Remove specific characters
echo moose | tr -d 'o'
# output: mse
echo moose | tr -d 'os'
# output: me
Squeeze character sequences
echo moooooossse | tr -s 'os'
# output: mose