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Accepted
yael
Asked: 2012-05-11 04:44:22 +0800 CST

perl + Match last number in file and reduce it by one

  • 772

I want to add the following perl command in my bash script please advice

how to change (reduce by one ) the last number that start with "+" character in file with perl ?

Example of original file   ( before run the perl command )

more file




432423
53454
+535
343
45
+1000

example of requested output file ( after run the perl command )

more file




432423
53454
+535
343
45
+999
solaris perl bash

2 Answers

  1. Best Answer

    When I hear "do something on the LAST occurrance of ...", I reach for tac to reverse the lines, and do something on the FIRST occurrance.

    tac file | nawk '/^\+/&&!done {$1 = "+" substr($1,2)-1; done=1} 1' | tac

    On Solaris, you may not have tac installed. You can implement it like this:

    tac() { sed -n -e '1!G' -e '$p' -e h "$@"; }
    • 2

  2. You can the following script:

    #!/usr/bin/perl -w
use strict;

open(INFILE, "< file") or die( "Can't open input file" );
open(OUTFILE, "> file.out") or die( "Can't open output file" );
my @lines = reverse <INFILE>;
foreach my $line (@lines) {
    if ($line =~ /^\+(\d+)/) {
        $line = "+".($1-1)."\n";
        last;
    }
}
my @lines2 = reverse @lines;
foreach my $line (@lines2) {
    print OUTFILE $line;
}
close(OUTFILE);
    • 1