I want to run a program requiring comma-separated arrays of files as follows:

program -input1 A.txt,B.txt,C.txt -input2 D.txt,E.txt,F.txt -out out.txt

My bash attempt:

I'm running command from a folder called ProgramFolder and this folder also contains file1.txt and file2.txt. file1.txt and file2.txt contain names of files for the program, such as:



But "A.txt, B.txt,C.txt" and "D.txt, E.txt,F.txt" are in a different folder: source 1 and source2 as shown below.

## file sources
source1= ~/Band/folder1/
source2= ~/Band/folder1/

I have tried running the program this way without success:

program -input $source1$(cat file1.txt) -input2 $source2$(cat file2.txt) -out out.txt

What is the best way to write a bash for running the program?

  • The easiest way is probably to include the paths in File1.txt and File2.txt and then use program -input1 $(cat File1.txt) -input2 $(cat File2.txt)
    – Wayne_Yux
    Aug 27, 2015 at 10:52

1 Answer 1


You may use sed inside the two command substitutions to process the original files prior their listing within the arguments of the program (thanks to steeldriver for the simplified pattern):

program -input "$(sed "s@^\|,@&$source1@g" file1.txt)" -input2 "$(sed "s@^\|,@&$source2@g" file2.txt)"

I changed the sed commands' default delimiter (/) to @ because both $source1 and $source2 will expand to a path containing /; nontheless | is needed for the alternation.

sed commands breakdown:

  • s: asserts to perform a substitution
  • @: starts the pattern
  • ^\|,: matches either the start of the line or a , character
  • @: stops the pattern / starts the replacement string
  • &: backreference which will expand to the match
  • $sourceN: expands to the content of $sourceN
  • @: stops the replacement string / starts the modifiers
  • g: substitutes every match in the line

Sample output of the sed commands for the given values of $source1, $source2 and for the given contents of file1.txt and file2.txt:

user@debian ~/tmp % echo $source1
user@debian ~/tmp % echo $source2
user@debian ~/tmp % cat file1.txt 
user@debian ~/tmp % cat file2.txt 
user@debian ~/tmp % sed "s@^\|,@&$source1@g" file1.txt
user@debian ~/tmp % sed "s@^\|,@&$source2@g" file2.txt
  • 1
    Does the match pattern really need to be that complicated? how about just sed "s@^\|,@&$source1@g" File1? Aug 27, 2015 at 12:00
  • @steeldriver Indeed... it doesn't: It was the result of many wrong attempts. Thanks! Updated
    – kos
    Aug 27, 2015 at 12:14
  • Many thanks to you two, Kos and steeldriver. The solution is perfect. Just what I wanted!
    – user27976
    Aug 27, 2015 at 13:47
  • @user27976 Glad that it helped :)
    – kos
    Aug 27, 2015 at 13:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.