perl one liner to print a line

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

Replies are listed 'Best First'.
Re: perl one liner to print a line by jwkrahn (Abbot) on Dec 12, 2008 at 01:43 UTC
`perl -ne'print if $. == 4' file.txt` [download]	[reply] [d/l]
Re^2: perl one liner to print a line by ikegami (Patriarch) on Dec 12, 2008 at 02:00 UTC
You can exit sooner with `perl -ne'print, last if $. == 4'` [download]	[reply] [d/l]
Re^3: perl one liner to print a line by jwkrahn (Abbot) on Dec 12, 2008 at 07:05 UTC
I prefer: `perl -ne'print and close ARGV if $. == 4' file.txt` [download] It works better with multiple files on the command line. `;-)`	[reply] [d/l] [select]
Re: perl one liner to print a line by ikegami (Patriarch) on Dec 12, 2008 at 01:58 UTC
The array approach would be `perl -e'@x=<>; print $x[3]'` [download] but that loads the entire file into memory where the `$.` method doesn't. Just putting it out there since you tried to use an array.	[reply] [d/l] [select]
Re^2: perl one liner to print a line by sugar (Beadle) on Dec 12, 2008 at 02:03 UTC
yea... i dont want to take the whole file into memory. so $. is a better way for me :)	[reply]
Re^2: perl one liner to print a line by jwkrahn (Abbot) on Dec 12, 2008 at 07:11 UTC
Or: `perl -F'\n' -lan0777e'print $F[3]' file.txt` [download]	[reply] [d/l]
Re: perl one liner to print a line by oko1 (Deacon) on Dec 12, 2008 at 02:37 UTC
And TMTOWTDI again: `perl -wne'print if 4..4' file.txt` [download] -- "Language shapes the way we think, and determines what we can think about." -- B. L. Whorf	[reply] [d/l]
Re: perl one liner to print a line by kyle (Abbot) on Dec 12, 2008 at 02:28 UTC
TIMTOWTDI... `perl -e '<> for 1..3; print scalar <>' file.txt` [download]	[reply] [d/l]
Re: perl one liner to print a line by Lawliet (Curate) on Dec 12, 2008 at 02:55 UTC
TMTOWTDI meets Occam's razor :P `perl -e 'print "one way to"'` I'm so adjective, I verb nouns! chomp; # nom nom nom	[reply] [d/l]
Re^2: perl one liner to print a line by sugar (Beadle) on Dec 12, 2008 at 04:02 UTC
:D	[reply]
Re: perl one liner to print a line by mr_mischief (Monsignor) on Dec 12, 2008 at 04:08 UTC
YAWTDI, this time with no whitespace in the source: `perl -e '{$_=<>;$.<4?redo:print}'` [download] That really does look kinda like line noise. I wouldn't recommend that for serious work, of course.	[reply] [d/l]
Re^2: perl one liner to print a line by ikegami (Patriarch) on Dec 12, 2008 at 04:20 UTC
4 chars shorter: `perl -ne'print,last,if$.==4' 12345678901234567890123 23` [download] Update: 5 chars shorter: `perl -nlE'say,last,if$.==4' 1234567890123456789012 22` [download]	[reply] [d/l] [select]
Re^3: perl one liner to print a line by jwkrahn (Abbot) on Dec 12, 2008 at 07:17 UTC
`perl -ne'4..4&&print'` [download]	[reply] [d/l]
Re^4: perl one liner to print a line by ikegami (Patriarch) on Dec 12, 2008 at 07:28 UTC
Re^3: perl one liner to print a line by mr_mischief (Monsignor) on Dec 12, 2008 at 15:07 UTC
I can save another character if we reintroduce whitespace: `perl -ne'$.-4or print,last'` [download] or almost identically: `perl -ne'$.<4or print,last'` [download] Update: `perl -nlE'$.<4or say,last' 123456789 123456789 1 21` [download]	[reply] [d/l] [select]
Re: perl one liner to print a line by telemachus (Friar) on Dec 12, 2008 at 13:14 UTC
Lots of people have suggested good ways to do it, but here are a few points about your original version. `perl -i -e 'while(<>){print $_[3];}' file.txt` [download] The -i switch says that you want to edit in place. Normally you use that like this: -i.bak. The .bak (or whatever else) becomes a suffix for a copy of your original file. The original becomes file.txt.bak and file.txt gets edited. If you use -i by itself without a suffix, then you don't get a backup. That's dangerous. Since you're not editing at all here, you don't want the switch. (In this example, if you had successfully done print if $. == 4 and used the -i switch with no suffix, you would get no backup and only line 4 left in your original file. I don't think that's what you wanted.) The -p and -n switches are worth looking at in perlrun since they will give you the while(<>) loop for free.	[reply] [d/l]
Re^2: perl one liner to print a line by ngungo (Initiate) on Jul 04, 2011 at 17:30 UTC
How about if I want to print the first line that match a regrex expression. Thanks, ngungo (newbie)	[reply]
Re^3: perl one liner to print a line by Anonymous Monk on Jul 05, 2011 at 10:57 UTC
Hi, new questions go in Seekers Of Perl Wisdom because telemachus, whom you asked a question, hasn't been here in 10 weeks. The node to which you replied is 2+ years old. Welcome, see The Perl Monks Guide to the Monastery, see How do I post a question effectively?, Where should I post X? See perlintro, Tutorials: Pattern Matching, Regular Expressions, and Parsing, perlretut, FMTYEWTK About Mass Edits In Perl, Uncommon* but Useful Perl Command Line Options for One-liners, Re^2: perl -pi -e s'/^\s+//'g $file	[reply]
Re: perl one liner to print a line (GOLF!) by ccn (Vicar) on Dec 12, 2008 at 07:14 UTC
`perl -lne 'die"$_\n"if$.==4'` [download] `perl -pe '$_=($.-4)?"":$_'` [download]	[reply] [d/l] [select]
Re^2: perl one liner to print a line (GOLF!) by ikegami (Patriarch) on Dec 12, 2008 at 07:24 UTC
`die"$_\n"` sends to STDERR, so you need to add " `2>&1`". The second doesn't do the same thing as the other golfs so far. It reads the entire file whereas the other golfs spent extra character to stop after 4 lines. If reading the entire file is ok, then I put forth `perl -lnE"$.^4\|\|say" 123456789012345 15` [download]	[reply] [d/l] [select]