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

Comfortable as I am with Perl CGI, DBI, OO, regexen, etc. ...*cough*, I treat command-line stuff as foreign turf.

Now I need to make a simple change in all files in all subdirectories of the current directory. So here is a learning opportunity. I have Camel at my elbow and the docs on the screen -- but the switch options are a bit dizzying.

Here's my attempt: %perl -ne 's/old/new/g' ./*/* This is mission-critical so I need to get it right. (I am backing up the whole mess.) Am I on the right track?

Replies are listed 'Best First'.
Re: Need one-liner to s///g in all sub-dirs
by rob_au (Abbot) on Aug 25, 2001 at 07:22 UTC
    Making use of other shell utilities, this is the most immediate solution which comes to mind for me:
     
    find . -type f -exec perl -pi.bak -e 's/old/new/g' {} \;

     
    If you want to do it 'all in Perl', find2perl makes it easier still:
     
    rob@budapest:~$ find2perl . -type f -exec perl -pi.bak -e 's/old/new/g
+' {} \;
#!/usr/bin/perl-5.005
    eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
        if $running_under_some_shell;

require "find.pl";

# Traverse desired filesystems


&find('.');

exit;
sub wanted {
    (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($_)) &&
    -f _ &&
    &exec(0, 'perl','-pi.bak','-e','s/old/new/g','{}');
}

sub exec {
    local($ok, @cmd) = @_;
    foreach $word (@cmd) {
        $word =~ s#{}#$name#g;
    }
    if ($ok) {
        local($old) = select(STDOUT);
        $| = 1;
        print "@cmd";
        select($old);
        return 0 unless <STDIN> =~ /^y/;
    }
    chdir $cwd;         # sigh
    system @cmd;
    chdir $dir;
    return !$?;
}

    [download]

     
    If you then wanted to take out the forking of a separate perl process for the editing of each file, then I would recommend changing the &exec() call to something similar to that posted by tachyon recently at Inplace Editing.
     

     
    Ooohhh, Rob no beer function well without!
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      dvergin struggles to follow the thread...
      Assuming I've already made the backups. What does find . -type f -exec perl -pi.bak -e 's/old/new/g' {} \; do that my suggestion does not do.

      And why '-p' instead of '-n'.

      Oops! Found another switch. I now submit: %perl -nie 's/old/new/g' ./*/*

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        Okay, the find . -type f -exec perl -pi.bak -e 's/old/new/g' {} \; command finds all files under the current directory and passes them through the command perl -pi.bak -e 's/old/new/g' {} which the {} delimiter is replaced with the filename. This I feel is the easiest way to find all files within a given directory tree and pass them through the perl command for in-place modification. Yes it isn't a "pure-Perl" solution, but sometimes reinventing the wheel isn't the best approach to a problem. And that too, as always, TIMTOWTDI.
         
        The -n and -p command line switches are similar, both creating a loop similar to this around the passed -e code:
         
        #   -n switch execution
#
LINE: while (<>) {
    ....    # your command is executed here
}

        [download]

         
        The difference is that the -p causes an additional print statement to be incorporated into the loop which is important so that your modified code is printed back out to the file. For example:
         
        #   -p switch execution
#
LINE: while (<>) {
    ....    # your command is executed here
    } continue {
        print;
    }
}

        [download]

         
        Assuming you have already made your backups, you can remove the -i.bak switch which would made a backup of modified files, moving then to name.bak.
         

         
        Update : The Perl command line switches are well documented at perlman:perlrun with additional examples.
         

         
        Ooohhh, Rob no beer function well without!
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Re: Need one-liner to s///g in all sub-dirs
by runrig (Abbot) on Aug 25, 2001 at 10:15 UTC
    Efficient and compact unix one liner (faster than using -exec on the find command) combining shell and perl, but dangerous if filenames contain newlines or other whitespace (I think some find's have an option to quote the output, but I haven't seen one yet):
    find . -type f | xargs perl -pi -e 's/old/new/g'

    [download]
    See perldoc perlrun for the -p and -i option and modify to '-pi.bak' or somesuch if you want a backup of all files.
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