Bash检查文件是否存在以及文件扩展

Question

I want to check if there is a file matching a given pattern exists in the target directory, thus write

data_dir="/home"
sample="HT001"
r1Pattern=".R1.gz"
shopt -s nullglob

if [ -f ${data_dir}/${sample}*combined${r1Pattern} ]
then
  ./myscript
fi

There is NO /home/HT001_combined.R1.gz exist. But this code kept telling me file exists. Is there anything I missed?

Thanks.

Answer 1

This is because of nullglob mode. Since the file does not exist, the glob expands to nothing. And, for an empty arguement, -f will return true if you use [ :

$ empty=
$ [ -f $empty ] && echo yes
yes

You can solve your problem by using the bash [[ instead:

$ [[ -f $empty ]] && echo yes

[[ generally provides more predictable and friendly behavior.

EDIT:

Yeah you are right, It seems that actually the glob is not evaluated when using [[ . The way that comes to mind to do it is more like:

f=(${data_dir}/${sample}*combined${r1Pattern})
if (( ${#f[@]} == 1 )) && [[ -f ${f[0]} ]]
then
    # ...
fi

This expands the glob into an array, makes sure there is exactly one result, and verifies that it is a regular file.