Assuming you've got your while loop set up right and you're doing inline editing... and that the only thing you need is to perform an edit on the first line, you could modify your "if" statement like this: 

$. == 1 && $aa =~ /LEU\b/ && s/    (.*)/$z31eu $z2leu $z1leu  $1/;

[download]

That way, only when $. (the filehandle line counter) equals zero (the first line of the file) you will actually modify the line. The rest of your iterations through the fils you'll basically skip the code that performs the substitution.

Remember, of course, that you do have to write each line anew. The most common strategy is to open the input file, open a temporary output file, read line by line from the input file as you write line by line to the output file. You must do this for every line of the file. And on the first line (in your case) you'll also perform additional modifications to the data. Finally, you close both files, and rename the temp file to the name of your input file.

Update: Changed $. == 0 to $. == 1 to correct the error pointed out by halley.


Dave

In reply to Re: substitutions on a single line by davido
in thread substitutions on a single line by indie_campbell

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