Seek, Copy & Paste

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Seek, Copy & Paste by KurtSchwind (Chaplain) on Nov 25, 2007 at 06:50 UTC
I'm not sure what OS you are in. But there is a unix command that does this for you. `comm -1 a.txt b.txt > c.txt` -- I used to drive a Heisenbergmobile, but every time I looked at the speedometer, I got lost.	[reply] [d/l]
Re^2: Seek, Copy & Paste by tachyon-II (Chaplain) on Nov 25, 2007 at 08:02 UTC
And (somewhat amazingly) you can do the same on Win32 from the command line although it does take 3 more keystrokes..... `findstr /g:a.txt b.txt > c.txt` [download]	[reply] [d/l]
Re^2: Seek, Copy & Paste by toolic (Bishop) on Nov 25, 2007 at 13:56 UTC
Keep in mind that the unix comm command requires its input files to be sorted first.	[reply]
Re^2: Seek, Copy & Paste by Anonymous Monk on Nov 25, 2007 at 15:15 UTC
Maybe better to use grep for that: `grep -f file_1 file_2 > file_3` [download]	[reply] [d/l]
Re: Seek, Copy & Paste by sh1tn (Priest) on Nov 25, 2007 at 09:58 UTC
`cat filename_1 filename_2 \| perl -ne '$_{$_}++ && print' -` [download] or just `perl -ne '$_{$_}++ && print' filename_1 filename_2` [download]	[reply] [d/l] [select]
Re^2: Seek, Copy & Paste by BrowserUk (Patriarch) on Nov 25, 2007 at 10:40 UTC
That will produce false hits if either file contains duplicates. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re: Seek, Copy & Paste by apl (Monsignor) on Nov 25, 2007 at 12:42 UTC
I can see the need for doing this in more than a one-liner. If you show us what you've already written, we can help you move it towards completion.	[reply]
Re: Seek, Copy & Paste by dwhite20899 (Friar) on Nov 26, 2007 at 00:28 UTC
Sounds like a homework problem, so I won't post code. Read the File1 names into the keys of a hash, read the File2 names in and check each to see if it is defined as a hash key, write the name to File3.	[reply]