Variable in curly braces not working

Question

I have a directory with country folders, where there might be folders that have doubled name:

 en_en es_es fr_fr de_de

And I wrote a script to remove the duplication:

 for code in en de es fr it nl pt tr; do
   if [[ -d $code_$code ]]; then
     mv "${code}_${code}" "${code}"
   fi
 end

But it doesn't work – the code under if never gets executed (I tried putting an echo there as well). However, the following works:

 if [[ -d es_es ]]; then
   echo "foo"
 end

I'm using (log)bash 3.2.

Answer 1

Because $code_$code is looking for code_ + code, while you want to check code+ _ + code. To do so, use braces: ${code}_${code}.

for code in en de es fr it nl pt tr; do
   if [[ -d "${code}_${code}" ]]; then # <---- here (note also it is good to quote)
     mv "${code}_${code}" "${code}"
   fi
end

This happens because _ can be present in the name of a variable, hence we use braces to define exactly what is the name when calling them.

See another example:

$ this=3
$ that=4
$ echo $this_$that
4
$ echo ${this}_${that}
3_4
$ this_=5
$ echo $this_$that
54