Command-line Perl
Command-line Perl
(Part 1)
or: Perl one-liners saved my career
or: `perldoc perlrun` brought to life
Perl code on the command line
Look Ma, no script!
_
$ perl print
# Can't open perl script \"print\": No such file or directory
-e (The `e` is for hysterical raisins)
_
$ perl -e print
# (No output)
Quoting on the command line
...and you can quote me on that
_
$ perl -e ' print \"Hello\\n\"; ' # Unix
$ perl -e \" print 'Hello' . $/; \" # Win32
$ perl -e \" print qq'Hello\\n'; \" # Win32; sick
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Command-line Perl
$ perl -e \" print qq{Hello\\n}; \" # Win32; better
Automatic end-of-line handling
# Calculator
$ perl -e ' print 42 * 42 '
1764$ perl -e ' print 42 * 42 * 42 '
74088$
The -l flag adds \"\\n\" to `print`
$ perl -le ' print 42 * 42 '
1764
$ perl -le ' print 42 * 42 * 42 '
74088
Defaults
@ARGV is the array of command-line arguments
shift takes @ARGV as its default
_
$ perl -le ' print @ARGV; $z=shift; print $z; ' foo bar baz
# foobarbaz
# foo
print takes $_ as default, and for sets $_ as default.
_
$ perl -le ' print for @ARGV ' foo bar baz
# foo
# bar
# baz
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Command-line Perl
Warnings
Double your money!
$ perl -l -e ' $zz = shift; print $z . $z ' 15
# (No output)
Always pay for the cheap insurance
$ perl -wle ' $zz = shift; print $z . $z ' 15
# Name \"main::zz\" used only once: possible typo at -e line 1.
# Use of uninitialized value in concatenation (.) or string at -e line 1.
# Use of uninitialized value in concatenation (.) or string at -e line 1.
Corrected
$ perl -wle ' $z = shift; print $z . $z ' 15
# 1515
Command-line Modules
-M means `use`
_
$ perl -MData::Dumper -wle 1
# (No output)
$ perl -MData::Dumper::Dear::John -wle 1
# Can't locate Data/Dumper/Dear/John.pm in @INC (@INC contains ...
$FOO::VERSION is a CPAN standard
_
$ perl -MData::Dumper -wle 'print $Data::Dumper::VERSION'
# 2.121_02
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Command-line Perl
Advanced preview
$ head -4 ~/Perl/Parrot/parrot_root_svn_q_log.txt
# ------------------------------------------------------------------------
# r38247 | chromatic | 2009-04-21 14:07:13 -0500 (Tue, 21 Apr 2009)
# ------------------------------------------------------------------------
# r38246 | fperrad | 2009-04-21 13:17:20 -0500 (Tue, 21 Apr 2009)
$ cut -s -d ' ' -f 3 ~/Perl/Parrot/parrot_root_svn_q_log.txt \\
| tr \"[:upper:]\" \"[:lower:]\" | sort | uniq -c | sort -nr
$ perl -wlane
$h{lc $F[2]}++ if @F>1; END{ printf \"%7d\\t%s\\n\", $h{$_}, $_
for sort { $h{$b} <=> $h{$a}} keys %h}
~/Perl/Parrot/parrot_root_svn_q_log.txt
# 4215 leo
# 2933 coke
# 2850 bernhard
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