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I have the following problem:

I want to use a loop to plot data from different files (named file1.dat, file2.dat, ... in this example) in just one output-plot. I use this in a shell script to do so:

plot for [i=1:6] u 1:2 'file'.i.'.dat'

Now I additionally want to only plot a certain range of lines from each file. To do this I learned to use:

plot "<(sed -n '1,100p' file.dat)"  u 1:2

Anyhow, if I want to combine these two like:

plot for [i=1:6] "<(sed -n '1,100p' file'.i.'.dat)"  u 1:2

clearly the i within the expression giving the filename file'.i.'.dat to sed cannot be interpreted as the variable i. The error I get is:

sed: can't read file_.i..dat: No such file or directory

Do you have any suggestions how to circumvent this problem or other approaches to achieve my goal?

  • 4
    if you're getting an awk error, then you're using awk and not showing us. Could you share enough of the script for someone else to be able to reproduce the issue? – Jeff Schaller Sep 7 '17 at 17:36
  • Did you try with matching quotes for i to be interpreted as variable: plot for [i=1:6] "<(sed -n '1,100p' file".i.".dat)" u 1:2? – sebasth Sep 7 '17 at 18:13
  • You should be able to use every ::0::99 to select the first 100 data points. – meuh Sep 7 '17 at 19:59
  • 2
    On a side note: sed -n 1,100p is better written as sed 100q. – Satō Katsura Sep 7 '17 at 20:04
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You have to change:

plot for [i=1:6] "<(sed -n '1,100p' file'.i.'.dat)"  u 1:2

to:

plot for [i=1:6] "<(sed -n '1,100p' file".i.".dat)"  u 1:2

Note how the quotes changed. The strings go from one double quote to another. In your line there is only one string <(sed -n '1,100p' file'.i.'.dat) which is not what you want. In my line, there are two strings <(sed -n '1,100p' file and .dat) that are concatenated with the value of i.

Besides, no need to resort to sed to print the first 100 lines of a file, this is typically a job for head (head -n 100).

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