Variable

Variable

Variable substitution within quotes

# foo=bar
 echo "'$foo'"
#'bar'
# double/single quotes around single quotes make the inner single quotes expand variables

Get the length of variable

var="some string"
echo ${#var}
# 11

Get the first character of the variable

var=string
echo "${var:0:1}"
#s

# or
echo ${var%%"${var#?}"}

Remove the first or last string from variable

var="some string"
echo ${var:2}
#me string

Replacement (e.g. remove the first leading 0 )

var="0050"
echo ${var[@]#0}
#050

Replacement (e.g. replace 'a' with ',')

{var/a/,}

Replace all (e.g. replace all 'a' with ',')

{var//a/,}

#with grep
 test="god the father"
 grep ${test// /\\\|} file.txt
 # turning the space into 'or' (\|) in grep

To change the case of the string stored in the variable to lowercase (Parameter Expansion)

var=HelloWorld
echo ${var,,}
helloworld

Expand and then execute variable/argument

cmd="bar=foo"
eval "$cmd"
echo "$bar" # foo