How can I save only a substring of file names from a directory without the file extension? - bash

Question

I have a directory that I'm reading from and I want to save only the date representation as a string.
I am close to getting it , although I know there is probably an easier way. Here is what I have so far:
#files are in the format of "THIS_20200420.csv" so I want only "20200420"
declare -a arr
declare -a arr2
FILES=test2/*.csv
for file in $FILES
do
arr=(${arr[*]} "${file##*/}")
done
for i in "${arr[#]}"
do
arr2+=$(echo $i | cut -c6-13)
done
for item in "${arr2[#]}"
do
echo $item
done
the output shows the array only having one element which is all the strings concatenated:
20200110202001202020021920200220202004202020042220200110202001202020021920200220202004202020042220200219202002202020042020200422
Im bashing my head against my computer at this point.

Answer 1

arr=(
"THIS_20200420.csv"
"THIS_20200421.csv"
"THIS_20200422.csv"
"THIS_20200423.csv"
"THIS_20200424.csv"
"THIS_20200425.csv"
"THIS_20200426.csv"
"THIS_20200427.csv"
"THIS_20200428.csv"
"THIS_20200429.csv"
"THIS_20200430.csv" )
arr=( ${arr[#]//*_} )
arr=( ${arr[#]//.*} )
echo "arr: ${arr[#]}"
Explanation:
arr=( ${arr[#]//*_} ) will match all char up to '_' for each element, and replace them with empty string.
arr=( ${arr[#]//.*} ) will match all char after '.' for each element, and replace them with empty string.
For more information on parameter expansion, a good reference is TLDP's guide on parameter expansion.

Answer 2

Try this
declare -a arrayname=($(ls -1 test2/*.csv | grep -o '[0-9]*'))
Demo:
$ls -1 *csv
THIS_20200420.csv
THIS_20200421.csv
THIS_20200422.csv
THIS_20200423.csv
THIS_20200424.csv
THIS_20200425.csv
THIS_20200426.csv
THIS_20200427.csv
THIS_20200428.csv
THIS_20200429.csv
THIS_20200430.csv
$declare -a arrayname=($(ls -1 *csv | grep -o '[0-9]*'))
$echo ${arrayname[#]}
20200420 20200421 20200422 20200423 20200424 20200425 20200426 20200427 20200428 20200429 20200430
$echo ${arrayname[2]}
20200422
$

Answer 3

You could achieve this using a loop with awk:
$ for file in *.csv; do echo $file | awk -F '[^[:alnum:]]' '{print $2}'; done
The -F '[^[:alnum:]]' tells awk to use non alphanumeric characters as the delimiter.
Another way to do this is to use bash shell parameter expansion to echo only the part of the filename you want. This obviously only works if your filenames have consistent formatting:
$ for file in *.csv; do echo "${file:5:8}"; done
I thought it would be nice to use bash parameter expansion to strip the unwanted prefix and suffix but you can't have nested expansion (afaict) so this is the best I could come up with:
$ for file in *.csv; do echo "$(tmp=${file%.csv}; echo ${tmp#THIS_})"; done

Answer 4

Meet Cut! A good friend of Linux Users
for file in ./*.csv; do echo $file | cut -d "_" -f 2 | cut -d "." -f 1 ; done
This one line should do the trick!
Example:

Answer 5

Use an array for the files assignment and parameter expansion.
#!/usr/bin/env bash
shopt -s nullglob
##: Save the files ending in *.csv in an array
## so it expands properly, variable assignment does not expand the glob *
files=(test2/*.csv)
##: Remain only the files that end with .csv without the pathname, longest match
files=("${files[#]##*/}")
##: Remain only the file names without the .csv extention
files=("${files[#]%.csv}")
##: Remain only the filename after the _ from the beginning, shortest match.
files=("${files[#]#*_}")
printf '%s ' "${files[#]}"