I think this should work for you (WARNING: I did it really quickly): 
#!/usr/bin/perl -w
use strict;

while (<DATA>) {
    s/^\/[\S]+\s//;
    print "$_\n";
}



__DATA__
INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090
/base-dir/dir/foo.txt INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090
INVALID ORDER-NO 4546090

[download]
This assumes your error msg will never start with /.

UPDATE: I knew I did this too fast:
  • I had a useless character class
  • didn't chomp THX tadman

    • so rewritten: 
    while (<DATA>) {
    chomp;
    s/^\/\S+\s//;
    print "$_\n";
}

    [download]


    grep
    grep> grep clue /home/users/*

    In reply to Re: A poor bloke and his regex... by grep
    in thread A poor bloke and his regex... by vek

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