ddrew78 has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks, I have a simple question to which I just can't seem to find the answer. First, here is what my file looks like (after several "sed" commands have already been executed): 
policy-map ipcos-abcde16
class abcde16-Queue1
priority police rate percent 35
class abcde16-Queue2
bandwidth 25
class abcde16-Queue3
bandwidth 15

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I am trying to insert a simple line break after the word "priority", so it would look like this: 
policy-map ipcos-abcde16
class abcde16-Queue1
priority 
police rate percent 35
class abcde16-Queue2
bandwidth 25
class abcde16-Queue3
bandwidth 15

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I have tried several variations of this command, but I either get nothing or a "sed: command garbled: s/priority/priority" error. I truly only need help with this one line :-( 
system "sed 's/priority/priority\n\/' cos2 > cos4";
system "mv cos4 cos2";

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And, before anybody asks, yes I am using strict and warnings. Any help would be appreciated.

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Re: inserting line break
by mr_mischief (Monsignor) on Apr 15, 2009 at 16:38 UTC

    Why shell to sed at all? 

    while ( <> ) {
    s/priority /priority\n/;
    print;
}

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    If you want it all in one line: 

    perl -i~ -pe 's/priority /priority\n/'

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    That second when given cos2 as an argument will read the input from cos2, write the output into cos2, and save the original contents as cos2~.

    You might want to see s/PATTERN/REPLACEMENT/msixpogce, perlre, perlrun (for the one-liner options), and perltrap which covers traps for people coming from awk, sed, C, and other languages.

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      Thanks, that worked perfectly.
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Re: inserting line break
by jethro (Monsignor) on Apr 15, 2009 at 16:51 UTC
    mr_mischiefs advice of using perl is really (really) the way to go. But to soothe your curiosity the error message is because of ...ity\n\/' which presumably should be ...ity\\n/'
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Re: inserting line break
by Bloodnok (Vicar) on Apr 15, 2009 at 17:30 UTC
    Using sed(1) to modify EOL chars is, AFAIR, only possible iff you've accumulated a number of lines (by appending them in, using the H command, to) the hold space e.g. the following will cause all lines in file to be output on the same line: 
    # sed -n 'H;$x;$s,\n,,gp' file
       ^  ^  ^  ^
       |  |  |  |
       |  |  |  |
       |  |  |  For the last line only, globally strip all line ending
+s in the pattern space and print the result
       |  |  |
       |  |  For the last line only, swap the hold and pattern spaces
       |  |
       |  Append each line to the hold space
       |
       Don't print any lines - by default all lines are printed follow
+ing processing

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    A user level that continues to overstate my experience :-))
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