How to modify words in a line using perl oneliner

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

Dear Monks,
I would like to modify the word "first" into "last" in the second line of file one.txt could you kindly help.

Input File(one.txt)

#verify_custom
fleet part=first base=first
after base
[download]

I tried the following perl one liner, but it did not help. perl -ni.bak -e 'print s/first/last/' one.txt

Expected Output:
#verify_custom
fleet part=last base=last
after base
[download]

Thanks a lot.

Comment on How to modify words in a line using perl oneliner Select or Download Code

Replies are listed 'Best First'.
Re: How to modify words in a line using perl oneliner by ccn (Vicar) on Sep 30, 2009 at 10:20 UTC
`perl -i.bak -pe 's/first/last/g' one.txt` [download] To make your code work you need to change the order of operators and add 'g' modifier to the regexp `perl -ni.bak -e 's/first/last/g; print' one.txt` [download]	[reply] [d/l] [select]
Re^2: How to modify words in a line using perl oneliner by BioLion (Curate) on Sep 30, 2009 at 11:10 UTC
Maybe also add in boundaries, just in case? Firstly, blast, etc... `perl -ni.bak -e 's/\bfirst\b/last/g; print' one.txt` Just a something something...	[reply] [d/l]
Re^2: How to modify words in a line using perl oneliner by Bloodnok (Vicar) on Sep 30, 2009 at 11:36 UTC
...or even, assuming ...second line... to be a specific requirement (c/w a statement of the loaction of the string to be changed): `perl -ni.bak -e 's/first/last/g if $. == 2; print' one.txt` [download] A user level that continues to overstate my experience :-))	[reply] [d/l]
Re: How to modify words in a line using perl oneliner by vitoco (Hermit) on Sep 30, 2009 at 14:21 UTC
What you are printing is the number of substitutions on each line, ie. "1" when "first" is found, and undef (nothing) when not. A value of "2" would be returned for line 2 if "g" modifier were used. Prefer `-p` option instead of `-n` for this kind of one-liners. In this case, the output should be: `perl -pi.bak -e 's/first/last/' one.txt #verify_custom fleet part=last base=first after base` [download] realizing that "g" modifier is missing if both "first" words must be changed at the same time.	[reply] [d/l] [select]