Sunday, November 22, 2009

Perl One-liners - An easy way to begin using Perl

A Perl one-liner is a small perl script run from the command-line prompt or a shell script as one command. You can pack a lot of power in a small command. By embedding Perl into a shell script you can enhance the capabilities of your shell script a great deal.

Here are some examples:

Fixed Length Data File - Show records where a column range matches a given string.

General Command:

perl -ne 'print if substr($_, StartCol, Stringlen) =~ "searchstring";'  infile.txt > outfile.txt

Example: Find records where position 488-489 is equal to "CA". Keep in mind that for startcol, the first character of the record begins a position 0.

perl -ne 'print if substr($_, 487, 2) =~ "CA";' infile.txt > outfile.txt

Pipe-Delimited Data File - Show records where a column 2 value equals 2


perl -ne 'split(/\|/); @line=@_; print if $line[1] == 2;' in.txt > out.txt

Korn shell - Embed Perl for loop inside Korn shell for loop

Example: Loop to count from 1 to 99 (by Odd numbers)
Note: everything between $( ... )  is the perl one-liner

for i in $(perl -e 'for ($i=1; $i<100; $i+=2) {print "$i\n";}')
  echo $i

Frequency Counter - Pipe Standard Input into this one-liner File of votes with a name on each line - in.txt

cat in.txt | perl -e '%freq;while (<>) {chomp;$freq{$_}++;} printf("%-40s %10i\n", $_, $freq{$_}) foreach sort keys %freq;'

Al               3
Fred           5
Mary         6