I am trying to make a .txt file that contains only one line gathered from other 30 .log files. To extract only one line I used this:

$ sed -n '/Num mapped reads/p' /home/travc/seq_v2/AgamP4_v2/samples/ERS224561/qualimap/qualimap.log > /data/home/odkirling/Mali/Yeah1.txt

It works great but now I need to do it for other 29 files, how can I do that?

  • 1
    What are those other 29 files named? One simplistic solution would be to just repeat that command for the other 29 filenames. Is there a filename pattern that's common to those 30 files and only to those files?
    – Jeff Schaller
    Nov 14, 2018 at 20:55
  • Can you provide a bit more information on the directory structure where the log files are located?
    – Jyotish P
    Nov 14, 2018 at 20:57
  • This is the path for the file home/travc/seq_v2/AgamP4_v2/samples/ERS224561/qualimap/qualimap.log. The only thing that changes is the name of the file "ERS224561"
    – user117970
    Nov 14, 2018 at 20:58
  • Please do not add details in a comment. Add them in an edit to your question.
    – DopeGhoti
    Nov 14, 2018 at 21:28
  • There's a tool that was designed specifically for this kind of job, it's called grep. Nov 14, 2018 at 21:41

2 Answers 2


You can try something like

for filepath in $(ls -1 /home/travc/seq_v2/AgamP4_v2/samples/*/qualimap/qualimap.log);
  sed -n '/Num mapped reads/p' $filepath >> /data/home/odkirling/Mali/Yeah1.txt

This will need the path before and after * to be exactly the same.


If your files are in a sequence, say ERS224561 to ERS224591, you can use seq 61 91. In this case, the script will be

for filenum in $(seq -w 30 150);
  sed -n '/Num mapped reads/p' "/home/travc/seq_v2/AgamP4_v2/samples/ERS2245$filenum/qualimap/qualimap.log" >> /data/home/odkirling/Mali/Yeah1.txt

Or let's say you have a list of directories in a text file, in the following format


then you can do something like

for dirname in $(cat dir_names.txt);
  sed -n '/Num mapped reads/p' "/home/travc/seq_v2/AgamP4_v2/samples/$dirname/qualimap/qualimap.log" >> /data/home/odkirling/Mali/Yeah1.txt

dir_names.txt is the file containing your directory names. Similarly, you should be able to replace any part of the file path based on your requirements.

  • Jyotish, Thanks that works great. The only concern I have is that your code extracts the info from my whole database. What if I want to extract info from 30 out of 150 files?
    – user117970
    Nov 14, 2018 at 22:35
  • Updated the answer. Hope it helps.
    – Jyotish P
    Nov 15, 2018 at 7:17
  • Thanks a lot, that is exactly what I needed and works perfectly!
    – user117970
    Nov 17, 2018 at 19:55

sed operates on an input stream that doesn't need to be limited to a single file; use multiple files instead, e.g. by supplying wild card characters in the files' paths like .../ERS*/.../*log

  • Thanks. So, that means that I have to write the name of each file li this /filename/ filename/ filename/...n/
    – user117970
    Nov 14, 2018 at 22:24
  • Try to analyse, understand and apply my example.
    – RudiC
    Nov 14, 2018 at 22:29
  • Thanks, i am trying to understand but i do not...
    – user117970
    Nov 14, 2018 at 22:33
  • @user117970 - well, this is the better answer but any absolute novice would have troubles understanding it... you need to do some serious reading up on globs/wildcards/filename patterns in order to understand it (at which point you will no longer ask this kind of question). Also, as I said above, the tool used here (sed) isn't the most suited for this task (though it does the job fine, no question). Nov 15, 2018 at 12:15

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