dboles@ccwf.cc.utexas.edu (David Boles) (05/24/91)
Warning: PERL NOVICE approaching !!!
I am trying to do the following file manipulation:
p220 p220 20 5
p220 p235 20 7
etc.
==>
p220 -20 -5
p220 20 5
p220 -20 -7
p235 20 7
etc.
I am using:
while (<>) {
s/(p\d*) (p\d*) (\d*) (\d*)/$1 -$3 -$4\n$2 $3 $4\n/;
print;
}
and I get:
p220 - -
p220 20 5
p220 - -
p235 20 7
etc.
If I take away the minus signs in the replacement string, I just get:
p220
p220 20 5
p220
p235 20 7
etc.
Why aren't $3 and $4 "alive" in the first half of the replacement
string? What am I missing?
Thanks!
David Boles
--
-------------------------------------------------------------------------------
David Boles Applied Research Laboratories
dboles@ccwf.cc.utexas.edu
apas611@chpc.utexas.edu This space for rent, apply within.
-------------------------------------------------------------------------------sherman@unx.sas.com (Chris Sherman) (05/24/91)
In <49420@ut-emx.uucp> dboles@ccwf.cc.utexas.edu (David Boles) writes: >Warning: PERL NOVICE approaching !!! Warning: PERL NOVICE answering!!! >I am trying to do the following file manipulation: >p220 p220 20 5 >p220 p235 20 7 >etc. > ==> >p220 -20 -5 >p220 20 5 >p220 -20 -7 >p235 20 7 >etc. >I am using: >while (<>) { > s/(p\d*) (p\d*) (\d*) (\d*)/$1 -$3 -$4\n$2 $3 $4\n/; > print; >} >and I get: >p220 - - >p220 20 5 >Why aren't $3 and $4 "alive" in the first half of the replacement >string? What am I missing? I think I got it. Perl is taking your test string literally, space for space. The synchronization is lost. I used the following input file with your code: p220 p220 20 5 p220 p235 20 7 and got: p220 -20 -5 p220 20 5 p220 -20 -7 p235 20 7 So then I tried the following code: #!/usr/local/bin/perl while (<>) { s/(p\d*) *(p\d*) *(\d*) *(\d*)/$1 -$3 -$4\n$2 $3 $4\n/; print; } With the following input: p220 p220 20 5 p220 p235 20 7 and got p220 -20 -5 p220 20 5 p220 -20 -7 p235 20 7 Maybe perl pro's can tell me what the '*'s meant exactly, why they are working, and if they would work in every case. (I have my ideas, but they are probably wrong, and I just got lucky. I was hoping to set up a one-or-more-number-of spaces type thing, but I don't think I did that right). -- Chris Sherman .................... sherman@unx.sas.com | ,-----------------------------------------' / Q: How many IBM CPU's does it take to execute a job? | A: Four; three to hold it down, and one to rip its head off.
lamour@gong.mitre.org (Michael Lamoureux) (05/24/91)
In article <sherman.675057031@foster>, sherman@unx.sas.com (Chris Sherman) writes: |> In <49420@ut-emx.uucp> dboles@ccwf.cc.utexas.edu (David Boles) writes: |> |> >Warning: PERL NOVICE approaching !!! |> |> Warning: PERL NOVICE answering!!! Ditto. (But I am avidly reading the book...) |> >I am using: |> >while (<>) { |> > s/(p\d*) (p\d*) (\d*) (\d*)/$1 -$3 -$4\n$2 $3 $4\n/; |> > print; |> >} |> >Why aren't $3 and $4 "alive" in the first half of the replacement |> >string? What am I missing? |> |> I think I got it. Perl is taking your test string literally, space |> for space. This is exactly it. |> #!/usr/local/bin/perl |> while (<>) { |> s/(p\d*) *(p\d*) *(\d*) *(\d*)/$1 -$3 -$4\n$2 $3 $4\n/; |> print; |> } |> |> Maybe perl pro's can tell me what the '*'s meant exactly, why |> they are working, and if they would work in every case. |> I was hoping to set up a one-or-more-number-of |> spaces type thing, but I don't think I did that right). Well, your expression tests for 0 or more spaces. An "*" tests for 0 or more occurences, a "+" tests for 1 or more. So using "+" instead of "*" would fix that, but I think using a "\s" instead of a " " would be more multi-purpose. This matches any whitespace, not just a space. So I guess it should look like this: while (<>) { s/(p\d+)\s+(p\d+)\s+(\d+)\s+(\d+)/$1 -$3 -$4\n$2 $3 $4\n/; print; } This matches the p's only if they have numbers appended as well. So even better... while (<>) { if (/.*(p\d+)\s+(p\d+)\s+(\d+)\s+(\d+).*/) { print "$1 -$3 -$4\n$2 $3 $4\n"; } } This allows you to put comments or something else in the file and only prints out the strings which match (and drops typos...you may want to change this expression a bit and flag errors with an else). Note that "." matches any character. Michael lamour@mitre.org Disclaimer: Perl is addictive ;-)