Am learning bash and it's confusing how (why) this line of code if [$1 = ]; then works. Can someone please explain.
From bash tuturial here under File re-namer (6th block)
# a quick check to see if any files were given
# if none then it's better not to do anything than rename some non-existent
# files!!
if [$1 = ]; then
echo "no files given"
exit 0
fi
That code is wrong, it does not work if the argument is not empty (and does not begin with whitespace) because [ is not a special character and is not recognised as command if it is not a separate word (that would not even work with [[).
set -x shows you what the shell sees:
set -x
[$1 = ]
+ '[' = ']'
In that case the test result is true because there is a string between [ and ]; it does not matter that it is =.
Tests for a non-empty argument should be done as
[ -n "$1" ] ; echo $?
+ '[' -n '' ']'
+ echo 1
or
[ -z "$1" ] ; echo $?
+ '[' -z '' ']'
+ echo 0
instead
