Re: One liner to S & R by column

What have you tried?

perl -pli.bak -e '$. != 1 and substr($_,18, 1) =~ tr/Y/H/;' filename

Here's how to read it:

Run perl.
Open filename for reading.
Rename the input file filename.bak Open filename for output and select it as the default for STDOUT.
Form an implicit while( <> ) { chomp; ... } continue { print "$_$/" } loop.
If $. is 1 (first line of the file), skip to the next iteration.
On all subsequent iterations $. will no longer be one; transliterate the 18th (zero-indexed) column from 'Y' to 'H'.

perlrun, perlintro, and perlop should contain 99% of what you need to learn to get a good start on the next one-liner yourself.

Update: Added play by play explanation.

Update2: Fixed issue where files aren't zero-indexed with respect to $. (Thanks Jim,Laurent_R)

Dave

Comment on Re: One liner to S & R by column Select or Download Code

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Re^2: One liner to S & R by column by Jim (Curate) on Dec 23, 2013 at 17:54 UTC
If $. is 0 (first line of the file), skip to the next iteration. … On all subsequent iterations $. will no longer be zero… The number of the first line of the input file is 1, not 0. So you need to use an explicit comparison operation. `perl -pli.bak -e 'substr($_, 18, 1) =~ tr/Y/H/ if $. > 1' filename` [download] Here's the same thing using a regular expression. `perl -pli.bak -e 's/^.{18}\KY/H/ if $. > 1' filename` [download] Jim	[reply] [d/l] [select]
Re^3: One liner to S & R by column by davido (Cardinal) on Dec 23, 2013 at 18:01 UTC
Updated (and documented the change). :) Thanks. Dave	[reply]
Re^4: One liner to S & R by column by Laurent_R (Canon) on Dec 23, 2013 at 18:51 UTC
Hi, you still have this sentence in your original post: "On all subsequent iterations $. will no longer be zero." You will probably want to fix it.	[reply]
Re^2: One liner to S & R by column by dirtdog (Monk) on Dec 23, 2013 at 17:15 UTC
Thank you Dave. That worked like a charm!	[reply]