How can I read and print lines that has only one word from a file

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

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Re: How can I read and print lines that has only one word from a file by cjf (Parson) on Jul 15, 2002 at 03:35 UTC
So you want to open a file and print out all lines that only contain one word? If so, this should work: `open FILE, "file.txt" or die $!; while (<FILE>) { chomp; print "$_\n" if $_ =~ /^(\w+)$/; } close FILE;` [download] Let me know if you have any questions. Update: ++'s to tadman for the improvements below.	[reply] [d/l]
Re^2: How can I read and print lines that has only one word from a file by tadman (Prior) on Jul 15, 2002 at 04:17 UTC
Or alternatively, being a little more accomodating: `while (<>) { print if (/^\s\S+\s$/); }` [download] You can call this with either one file, or as many as you like. The double-angle-brackets just read in anything from `@ARGV`. Further, it looks for a single group of "non-space" characters. This includes things with punctuation and such.	[reply] [d/l] [select]
Re: Re: How can I read and print lines that has only one word from a file by Anonymous Monk on Jul 15, 2002 at 04:30 UTC
Yes I have a question. Does /^(\w+)$/ mean that lines that start with one word or contain one word?	[reply]
Re^3: How can I read and print lines that has only one word from a file by tadman (Prior) on Jul 15, 2002 at 04:43 UTC
It means, literally, "start of line(^), followed by one-or-more word-characters(\w+), followed by end of line($)". This is one possible definition of "one word on line".	[reply]
Re: How can I read and print lines that has only one word from a file by jmcnamara (Monsignor) on Jul 15, 2002 at 07:16 UTC
Here is one way: `perl -nae 'print if @F == 1' file` And here is another: `awk 'NF == 1' file` -- John.	[reply] [d/l] [select]
Re^2: How can I read and print lines that has only one word from a file by Aristotle (Chancellor) on Jul 15, 2002 at 14:13 UTC
++! But don't forget to mention that perlrun is the place to look at when you hit a novice with such a solution. `:-)` Makeshifts last the longest.	[reply]