Linux

Bash read file names from a text file and take action

December 3, 2018
3 Min Read
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I need to read a list of file names from a text file named input.txt and take action each file name. How do I read file names from a text file and say run /bin/foo command on each file? How do I read filenames from a text file and take certain action on those files?

Introduction – Often you need to read a file line-by-line and process data. It is a pretty common task for Linux and Unix sysadmin shell scripts. You need to use a bash while loop and the read command.

Bash read file names from a text file

The syntax is as follows to read filenames from a text file:

while IFS= read -r file; do
  echo "Do something on $file ..."
done < "filenames.txt"

OR

input="data.txt"
while IFS= read -r file; do
  printf '%sn' "$file"
done < "$input"

Read filenames from a text file using bash while loop

Let us create a new file named input.txt with the filename on each line using the cat command or vim command:
cat > input.txt
Append data:

foo.txt
bar.txt
delta.jpg
nixcraft.logo.png
sales.pdf
/etc/resolv.conf
/home/vivek/Documents/fy-19-2020.ods
#/home/vivek/Documents/yearly-sales-data.ods

Related: How To Create Files in Linux From a Bash Shell Prompt

Here is a sample bash shell script to read a file line-by-line:

#!/bin/bash
# Name - script.sh
# Author - Vivek Gite under GPL v2.x+
# Usage - Read filenames from a text file and take action on $file 
# ----------------------------------------------------------------
set -e
in="${1:-input.txt}"
 
[ ! -f "$in" ] && { echo "$0 - File $in not found."; exit 1; }
 
while IFS= read -r file
do
	echo "Working on $file ..."
done < "${in}"

Simple run it as follows:
./script.sh
Bash read file names from a text file and take action

It is also possible to ignore filenames starting with #

Here is an updated version of the script:

#!/bin/bash
# Name - script.sh (bash read file names list from file)
# Author - Vivek Gite under GPL v2.x+
# Usage - Read filenames from a text file and take action on $file 
# ----------------------------------------------------------------
set -e
in="${1:-input.txt}"
 
[ ! -f "$in" ] && { echo "$0 - File $in not found."; exit 1; }
 
while IFS= read -r file
do
	## avoid commented filename ##
	[[ $file = #* ]] && continue
	echo "Running rm $file ..."
done < "${in}"

Conclusion

You learned how to read a list of filenames from a file in bash and take action on them.

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