How can I keep an extracted value in a variable in bash

Question

I have to extract certain values from some filenames in a directory and I wish to have a command to keep the extracted value in a variable. Say my files have the format place.type-date.log and I wish to extract and keep place in a variable called first, how can I do it?

I tried to use

first=$($file | awk -F'[.-]' '{print $1}')

but it didn't work.

Normally if I do

echo " place.type-date.log" | awk -F'[.-]' '{print $1}'

and the result will be place. So I just replaced place.type-date.log by $file in my command because I have to do it for multiple files in a particular directory where I used a for loop.

I want to store the extracted value place in the variable first that is why I equated the extraction command to the variable first. So when I tried to echo first, and I executed my script, it didn't show anything meaning the extracted value had not been stored in the variable.

Answer 1

Suppose you have a filename like place.type-date.log in the variable file, and you want to store the part of the filename before the first dot in another variable called first. In that case, you may do that using a standard parameter substitution.

first=${file%%.*}

The above removes the longest suffix matching the shell pattern .* from the value of $file and stores the result in first.

Using % in place of %% would remove the shortest matching suffix instead, leaving place.type-date. Using # or ## in place of % and %% would remove prefix strings rather than suffix strings.

For another example of using these substitutions, see my answer to your previous question.

---

Your code does not work because $file is the string place.type-date.log, not a command. You may have attempted to do something like

first=$( echo "$file" | awk -F '[.-]' '{ print $1 }' )

But this is more complicated than it needs to be. It also has some issues regarding escape sequences in filenames (which echo may expand) and filenames containing newlines (awk is a line-oriented text processing tool).