从文件名中删除开头的 4 个字母和结尾的 4 个字母

Question

I would like to have a command that could strip the starting 4 letters and ending 4 letters from a filename. For ex: if the file name is: form1234.tgz I would like to get the number 1234 from the file name. Can someone suggest, a simple way this could be done on Linux on the command prompt?

Answer 1

Removing the first four characters is easy using cut . Unfortunately, it doesn't have a built in way to remove characters from the end of a string, but you could always reverse it using rev apply cut and then rev it back again.

$ echo $FILENAME | cut -c5- | rev | cut -c5- | rev

Answer 2

Use parameter substitution.

filename=form1234.tgz
short=${filename#????}
short=${short%????}

# removes from the left, % removes from the right.

Answer 3

You can use a lot of options actually...

For this kind of things it would be better to match what you want instead of removing what you don't need: a typo could happen, or an already truncated file may be there...

For example, if you want to get rid of the extension, you can use parameter expansion , already supported in virtually every shell:

printf "%s" "${file%.*}"

If you need only numbers you can use a regular expression :

printf "%s" "${file}" | sed -e "s/.*\([0-9]*\)\..*/\1/"

Let's say that your question is way generic and does not provide a lot of information of what you want...

If you want to statically remove the first and last 4 chars, you can use parameter expansions, sed , cut , awk or whatever you want...

For example with sed, it would be something like:

printf "%s" "${file}" | sed -e "s/^....\(.*\)....$/\1/"

With paramete expansion would be:

file="${file#????}"
file="${file%????}"
printf "%s" "${file}"

And finally, if you are in a pure bash environment, you can simply use some of bash parameter expansion (Note that this option will not work everywhere):

printf "%s" "${file:4:-4}"

Note that every printf could (obviusly) be replaced by echo (or echo -n ).

Answer 4

Probably the easiest if you know how many chars to strip off the beginning and the end.

name=form1234.tgz

echo "${name:4:$((${#name} - 8))}"

1234