one-liners

[Michael Fowler]

I just had a few one-liners I found useful as of late, and wanted to share.


Recently, I decided to change from 8-space tabs using a tab character to
4-space tabs using spaces.  Needing to convert some pre-existing code I was
editing, I wrote a small script.  The script in actually written in sh, and
does the following (basically):

    mv $1 $1.bak
    expand $1.bak | unexpand | expand --initial -t 4 > $1

Given a filename as an argument, it renames the file, converts all tabs into
8 spaces (using tabstops, so alignment is kept), then converts all leading
whitespace to tabs (thus internal whitespace is maintained), then
re-converts any leading tabs to 4 spaces.  The extra steps are required to
maintain formatting; often I use tabs to line things up, e.g.

    my $foo     =  "bar";
    my $bar     =  "foo";

If those are tab characters, and all tabs are arbitrarily converted to 4
spaces, things no longer properly line up.

Here's the Perl equivalent:

    perl -MText::Tabs -i.bak -pnwe '$tabstop = 8; $_ = expand($_);
    s/^(\s+)/unexpand($1)/e; $tabstop = 4; $_ = expand($_);' filename

This has the advantage of being able to process multiple files listed on the
command-line, with no extra work.  The shell script, on the other hand,
would require modification.



Recently, I was messing around with Apache logfiles, and needed to check
what domains were in a given logfile.

    perl -anwe '$domains{$F[1]}++;  END { while (my($domain, $count) =
    each(%domains)) { printf("%4d  %s\n", $count, $domain) } }'

This prints out a list of the domains in the logfile, and how many
occurrences there were.


Michael
--
Administrator                      www.shoebox.net
Programmer, System Administrator   www.gallanttech.com
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