test if "$x" is not empty
Code:
if [ -n "$x" ]; then
...
else
...
fi
test if "$x" is empty (has a length of zero) :
Code:
if [ -z "$x" ]; then
...
else
...
fi
or (if $x has a length of zero)
Code:
if [ ${#x} -eq 0 ]; then
...
else
...
fi
Code:
# a=
# [[ ${#a} -eq 0 ]] && echo yes || echo no
yes
# a=x
# [[ ${#a} -eq 0 ]] && echo yes || echo no
no
# a=123
# [[ ${#a} -eq 0 ]] && echo yes || echo no
no
# a=0
# [[ ${#a} -eq 0 ]] && echo yes || echo no
no
You could also consider the following :
Code:
[[ -z "$a" ]] && echo Empty || echo NotEmpty
[[ ! -z "$a" ]] && echo NotEmpty || echo Empty
[[ -n "$a" ]] && echo NotEmpty || echo Empty
In fact the doublequote enclosing the $a are not necessary in [[ ]] (ksh and bash)
