One-liner to append text at fixed column

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

I wanted to be able to mark lines with comments at a fixed column an came up with this one-liner solution.

Did I miss a more elegant solution?

|perl -pe 'substr $_, -1, 0, " "x(68-length$_) . " #:$1" if /(^#|nextstate|var\d+)/;'

Explanation:

-p loop over input and print $_ at the end of -e evalcode
substr is inserting the text just before the newline (index -1, length 0)
" " x (68 - length $_) fills in space till column 68
" #:$1" inserts the match at column 70
if line $_ longer than 68 char, append the match after two spaces

example with column 50

$ perl -MO=Concise,-src tst_b_xref4.pl|perl -pe 'substr $_, -1, 0, " "
+x(48-length$_) . "  #:$1" if /(^#|nextstate|var\d+)/;'
tst_b_xref4.pl syntax OK
j  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
# 1: for (                                       #:#
2     <;> nextstate(main 3 tst_b_xref4.pl:1) v:{ ->3  #:nextstate
4     <1> preinc[t2] vK/1 ->5
-        <1> ex-rv2sv sKRM/1 ->4
3           <#> gvsv[*var1] s ->4                #:var1
[download]

Use case: Re^12: B::Xref buggy?

update

a bit shorter |perl -pe 'chomp, $_.=" "x(48-length$_) . " #:$1\n" if /(^#|nextstate|var\d+)/;'

update

meh, I expected a printf solution to be shorter

|perl -pe 'chomp, printf ("%-48s #:$1\n",$_), $_="" if /(^#|var|nextstate)/'

update

|perl -pe 'chomp, $_ = sprintf "%-48s #:$1\n",$_ if /(^#|var|nextstate)/'

IMHO best solution so far. :)

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery
FootballPerl is like chess, only without the dice}

Comment on One-liner to append text at fixed column Select or Download Code

Replies are listed 'Best First'.
Re: One-liner to append text at fixed column by jwkrahn (Abbot) on Nov 15, 2018 at 22:51 UTC
`perl -lne 'printf "%-48s%s\n", $_, /(^#\|nextstate\|var\d+)/ ? " #:$1" +: ""'` [download]	[reply] [d/l]
Re^2: One-liner to append text at fixed column by LanX (Saint) on Nov 15, 2018 at 22:58 UTC
ah yes -l for chomp. Thanks! :) `\|perl -lpe '$_= sprintf "%-48s #:$1",$_ if /(^#\|nextstate\|var\d+)/'` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l]
Re: One-liner to append text at fixed column by Veltro (Hermit) on Nov 16, 2018 at 12:18 UTC
Fiddling around a bit, trying to find a solution where it becomes more clear what is being searched for and which characters are being replaced. But still, it is not very pretty. `$_ = "abc_something" ; print $_ . "\n" if /abc/ && substr( $_, 0, 4 ) =~ s/(.+)/" "x((length $1)+2)."#:"/e ;` [download] The substr just takes care of replacing the first part with `" #:"`. Make sure that the search for 'abc' is done before doing the replacement since it is greedy.	[reply] [d/l] [select]
Re^2: One-liner to append text at fixed column by LanX (Saint) on Nov 16, 2018 at 13:29 UTC
If it comes to readability I prefer my last sprintf solution with the twist of changing `if` to `and` . `perl -lpe " /(match1\|match2)/ and $_ = sprintf qq{%-68s #$1}, $_ "` Normally I don't like short-circuit expressions, but in this case it really helps clarifying what's happening. Demo: (win quoting) >perl -E"say '.' x rand(80) for 1..10" \|perl -lpe " /(.)/ and $_ = spr +intf qq{%-68s #$1},$_ " ...................................................................... +...... #. ...................... +#. ..................... +#. ...................................................................... +.... #. ......................................................... +#. ...................................... +#. ......................... +#. ........................................................ +#. ...................................................................... +... #. ......................... +#. [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]
Re^3: One-liner to append text at fixed column by Veltro (Hermit) on Nov 16, 2018 at 15:31 UTC
Ok, I think I did not understand the original problem. I thought you were trying to 'align' all the comments from a text like this: `perl -E"say '.' x rand(80) . '# test comment' for 1..3" ......................# test comment .................................# test comment ...................................................................... +....# test comment` [download] So eventually I came up with this which I think is too complex. perl -E"say '.' x rand(80) . '# test comment' for 1..10" \|perl -lpe " +/\s#(.)$\|$/ && ( substr( $_, $-[0], length($_) ) = qq{ }x(68 - $-[ +0] + 2) . qq{ #$1} ) ............................................... + # test comment .......................................................... + # test comment ....................................... + # test comment ............................................................ + # test comment ...................................................................... +.... # test comment ...... + # test comment ........................................ + # test comment ............................... + # test comment ................................................... + # test comment ................................... + # test comment [download] Maybe it can be rewritten with a printf but I will leave it with this.	[reply] [d/l] [select]
Re^4: One-liner to append text at fixed column by LanX (Saint) on Nov 16, 2018 at 15:55 UTC