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Complete Perl Programming Language book for modern system administrators
This comprehensive guide covers: - 22 chapters of practical Perl programming - Focus on system administration and automation - Modern Perl best practices and techniques - Real-world examples and production-ready code - 3 appendices with one-liners, gotchas, and resources The book targets experienced sysadmins, DevOps engineers, and automation specialists, demonstrating Perl's continued relevance in 2025 for text processing, system administration, and rapid development. 🤖 Generated with Claude Code Co-Authored-By: Claude <noreply@anthropic.com>
This commit is contained in:
David Liedle
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appendix-a-perl-one-liners-cookbook.md
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appendix-a-perl-one-liners-cookbook.md
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# Appendix A: Perl One-Liners Cookbook
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*"Sometimes the most powerful programs are the ones that fit on a single line."*
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Perl's conciseness and expressiveness shine brightest in one-liners—those magical incantations that transform data, search files, and automate tasks, all from the command line. This cookbook contains battle-tested one-liners for real-world system administration tasks.
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## Text Processing
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### Search and Replace
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```bash
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# Replace text in a file (in-place)
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perl -pi -e 's/old_text/new_text/g' file.txt
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# Replace with backup
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perl -pi.bak -e 's/old_text/new_text/g' file.txt
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# Replace only on lines matching a pattern
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perl -pi -e 's/old/new/g if /pattern/' file.txt
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# Replace across multiple files
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perl -pi -e 's/old/new/g' *.txt
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# Case-insensitive replace
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perl -pi -e 's/old/new/gi' file.txt
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# Replace with captured groups
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perl -pi -e 's/(\w+)\.old\.com/$1.new.com/g' file.txt
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# Replace newlines with commas
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perl -pe 's/\n/,/g' file.txt
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# Remove trailing whitespace
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perl -pi -e 's/\s+$//' file.txt
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# Convert DOS to Unix line endings
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perl -pi -e 's/\r\n/\n/g' file.txt
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# Convert Unix to DOS line endings
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perl -pi -e 's/\n/\r\n/g' file.txt
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# Replace multiple spaces with single space
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perl -pi -e 's/ +/ /g' file.txt
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# Remove blank lines
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perl -ni -e 'print unless /^$/' file.txt
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# Replace tabs with spaces
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perl -pi -e 's/\t/ /g' file.txt
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# URL encode
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perl -MURI::Escape -e 'print uri_escape($ARGV[0])' "hello world"
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# URL decode
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perl -MURI::Escape -e 'print uri_unescape($ARGV[0])' "hello%20world"
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# HTML encode
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perl -MHTML::Entities -e 'print encode_entities($ARGV[0])' "<h1>Title</h1>"
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# Base64 encode
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perl -MMIME::Base64 -e 'print encode_base64("text")'
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# Base64 decode
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perl -MMIME::Base64 -e 'print decode_base64("dGV4dA==")'
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```
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### Line Operations
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```bash
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# Print specific line number
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perl -ne 'print if $. == 42' file.txt
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# Print lines 10-20
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perl -ne 'print if 10..20' file.txt
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# Print every nth line
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perl -ne 'print if $. % 3 == 0' file.txt
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# Number all lines
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perl -pe '$_ = "$. $_"' file.txt
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# Print line before and after match
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perl -ne 'print $prev if /pattern/; $prev = $_' file.txt
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# Remove duplicate lines
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perl -ne 'print unless $seen{$_}++' file.txt
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# Print lines longer than 80 characters
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perl -ne 'print if length > 80' file.txt
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# Print shortest line
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perl -ne '$min = $_ if !defined $min || length($_) < length($min); END {print $min}' file.txt
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# Print longest line
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perl -ne '$max = $_ if length($_) > length($max // ""); END {print $max}' file.txt
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# Reverse lines (tac)
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perl -e 'print reverse <>' file.txt
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# Shuffle lines randomly
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perl -MList::Util=shuffle -e 'print shuffle <>' file.txt
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# Sort lines
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perl -e 'print sort <>' file.txt
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# Sort numerically
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perl -e 'print sort {$a <=> $b} <>' file.txt
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# Sort by column
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perl -e 'print sort {(split /\s+/, $a)[2] cmp (split /\s+/, $b)[2]} <>' file.txt
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```
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### Field and Column Operations
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```bash
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# Print first field (like cut -f1)
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perl -lane 'print $F[0]' file.txt
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# Print specific columns
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perl -lane 'print "@F[0,2,4]"' file.txt
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# Print last field
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perl -lane 'print $F[-1]' file.txt
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# Sum numbers in first column
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perl -lane '$sum += $F[0]; END {print $sum}' file.txt
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# Average of column
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perl -lane '$sum += $F[0]; $count++; END {print $sum/$count}' file.txt
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# Join fields with comma
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perl -lane 'print join(",", @F)' file.txt
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# Print fields in reverse order
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perl -lane 'print join(" ", reverse @F)' file.txt
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# Count fields per line
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perl -lane 'print scalar @F' file.txt
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# Print lines with exactly n fields
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perl -lane 'print if @F == 5' file.txt
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# Transpose rows and columns
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perl -lane 'push @{$c[$_]}, $F[$_] for 0..$#F; END {print "@$_" for @c}' file.txt
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# Convert CSV to TSV
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perl -pe 's/,/\t/g' file.csv
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# Parse CSV properly
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perl -MText::CSV -e 'my $csv = Text::CSV->new(); while (<>) {$csv->parse($_); print join("\t", $csv->fields), "\n"}' file.csv
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```
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## File Operations
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### File Management
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```bash
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# Find files modified in last 24 hours
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perl -e 'print "$_\n" for grep {-M $_ < 1} glob("*")'
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# Find files larger than 1MB
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perl -e 'print "$_\n" for grep {-s $_ > 1_000_000} glob("*")'
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# Rename files (add prefix)
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perl -e 'rename $_, "prefix_$_" for glob("*.txt")'
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# Rename files (change extension)
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perl -e 'for (glob("*.txt")) {$new = $_; $new =~ s/\.txt$/.bak/; rename $_, $new}'
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# Delete empty files
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perl -e 'unlink for grep {-z $_} glob("*")'
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# Create backup copies
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perl -e 'for (glob("*.conf")) {system("cp", $_, "$_.backup")}'
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# List directories only
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perl -e 'print "$_\n" for grep {-d $_} glob("*")'
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# List files recursively
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perl -MFile::Find -e 'find(sub {print "$File::Find::name\n" if -f}, ".")'
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# Calculate total size of files
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perl -e '$total += -s $_ for glob("*"); print "$total\n"'
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# Find duplicate files by size
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perl -e 'for (glob("*")) {push @{$files{-s $_}}, $_} for (values %files) {print "@$_\n" if @$_ > 1}'
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# Touch files (update timestamp)
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perl -e 'utime(undef, undef, $_) for glob("*.txt")'
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# Make files executable
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perl -e 'chmod 0755, $_ for glob("*.pl")'
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# Find broken symlinks
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perl -e 'print "$_\n" for grep {-l $_ && !-e $_} glob("*")'
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```
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### Content Analysis
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```bash
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# Count lines in file
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perl -ne 'END {print $.}' file.txt
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# Count words
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perl -ne '$w += split; END {print "$w\n"}' file.txt
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# Count characters
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perl -ne '$c += length; END {print "$c\n"}' file.txt
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# Frequency count of words
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perl -ne 'for (split) {$freq{lc $_}++} END {print "$_: $freq{$_}\n" for sort {$freq{$b} <=> $freq{$a}} keys %freq}' file.txt
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# Find longest word
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perl -ne 'for (split) {$max = $_ if length($_) > length($max)} END {print "$max\n"}' file.txt
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# Extract email addresses
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perl -ne 'print "$1\n" while /([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,})/g' file.txt
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# Extract URLs
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perl -ne 'print "$1\n" while m!(https?://[^\s]+)!g' file.txt
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# Extract IP addresses
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perl -ne 'print "$1\n" while /(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/g' file.txt
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# Extract phone numbers (US format)
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perl -ne 'print "$1\n" while /(\d{3}[-.]?\d{3}[-.]?\d{4})/g' file.txt
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# Check for binary files
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perl -e 'for (glob("*")) {print "$_\n" if -B $_}'
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# Find files containing text
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perl -e 'for $f (glob("*.txt")) {open F, $f; print "$f\n" if grep /pattern/, <F>; close F}'
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```
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## System Administration
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### Process Management
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```bash
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# Kill processes by name
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perl -e 'kill "TERM", grep {/processname/} map {/^\s*(\d+)/; $1} `ps aux`'
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# Show process tree
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perl -e 'for (`ps aux`) {/^(\S+)\s+(\d+)\s+\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+(.*)/ && print "$2 $3\n"}'
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# Monitor CPU usage
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perl -e 'while (1) {$cpu = `top -bn1 | grep "Cpu(s)"`; print $cpu; sleep 5}'
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# Show memory usage
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perl -ne 'print if /^Mem/' < /proc/meminfo
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# List open ports
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perl -ne 'print if /:[\dA-F]{4}\s+0{8}:0{4}/' < /proc/net/tcp
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# Show disk usage over threshold
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perl -e 'for (`df -h`) {print if /(\d+)%/ && $1 > 80}'
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# Parse system logs
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perl -ne 'print if /ERROR|WARNING/' /var/log/syslog
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# Count log entries by hour
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perl -ne 'if (/(\d{2}):\d{2}:\d{2}/) {$hours{$1}++} END {print "$_: $hours{$_}\n" for sort keys %hours}' /var/log/messages
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```
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### Network Operations
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```bash
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# Ping sweep
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perl -e 'for (1..254) {system("ping -c 1 -W 1 192.168.1.$_ &")}'
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# Extract MAC addresses
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perl -ne 'print "$1\n" while /((?:[0-9A-Fa-f]{2}:){5}[0-9A-Fa-f]{2})/g' file.txt
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# Parse Apache logs
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perl -ne '/^(\S+).*\[([^\]]+)\]\s+"([^"]+)"\s+(\d+)/ && print "$1 $2 $3 $4\n"' access.log
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# Count 404 errors
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perl -ne '$c++ if / 404 /; END {print "$c\n"}' access.log
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# Top IP addresses in log
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perl -ne '/^(\S+)/ && $ip{$1}++; END {print "$_: $ip{$_}\n" for (sort {$ip{$b} <=> $ip{$a}} keys %ip)[0..9]}' access.log
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# Monitor bandwidth (rough)
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perl -e 'while (1) {$rx1 = `cat /sys/class/net/eth0/statistics/rx_bytes`; sleep 1; $rx2 = `cat /sys/class/net/eth0/statistics/rx_bytes`; printf "%.2f KB/s\n", ($rx2-$rx1)/1024}'
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# Parse netstat output
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perl -ne 'print "$1:$2\n" if /tcp\s+\d+\s+\d+\s+([\d.]+):(\d+)/' < <(netstat -an)
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# DNS lookup
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perl -MSocket -e 'print inet_ntoa(inet_aton($ARGV[0]))' hostname
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```
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## Data Processing
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### JSON Operations
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```bash
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# Pretty print JSON
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perl -MJSON::PP -e 'print JSON::PP->new->pretty->encode(decode_json(<>))' file.json
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# Extract field from JSON
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perl -MJSON::PP -ne 'print decode_json($_)->{field}, "\n"' file.json
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# Convert JSON to CSV
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perl -MJSON::PP -ne '$j = decode_json($_); print join(",", @{$j}{qw(field1 field2 field3)}), "\n"' file.json
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# Filter JSON array
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perl -MJSON::PP -e '$j = decode_json(join "", <>); print encode_json([grep {$_->{age} > 18} @$j])' file.json
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# Merge JSON files
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perl -MJSON::PP -e '@all = map {decode_json(do {local $/; open F, $_; <F>})} @ARGV; print encode_json(\@all)' *.json
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```
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### XML Processing
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```bash
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# Extract XML tags
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perl -ne 'print "$1\n" while /<tag>([^<]+)<\/tag>/g' file.xml
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# Convert XML to text
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perl -pe 's/<[^>]*>//g' file.xml
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# Pretty print XML
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perl -MXML::Tidy -e 'my $tidy = XML::Tidy->new(filename => $ARGV[0]); $tidy->tidy(); print $tidy->toString()' file.xml
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# Extract attributes
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perl -ne 'print "$1\n" while /attribute="([^"]+)"/g' file.xml
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```
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### Database Operations
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```bash
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# Quick SQLite query
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perl -MDBI -e '$dbh = DBI->connect("dbi:SQLite:dbname=test.db"); print "@$_\n" for @{$dbh->selectall_arrayref("SELECT * FROM users")}'
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# Export to CSV
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perl -MDBI -e '$dbh = DBI->connect("dbi:SQLite:dbname=test.db"); $sth = $dbh->prepare("SELECT * FROM users"); $sth->execute(); while ($row = $sth->fetchrow_arrayref) {print join(",", @$row), "\n"}'
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# Import from CSV
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perl -MDBI -MText::CSV -e '$csv = Text::CSV->new(); $dbh = DBI->connect("dbi:SQLite:dbname=test.db"); while (<>) {$csv->parse($_); $dbh->do("INSERT INTO users VALUES (?, ?, ?)", undef, $csv->fields)}'
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```
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## Date and Time
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```bash
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# Current timestamp
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perl -e 'print time, "\n"'
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# Current date
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perl -e 'print scalar localtime, "\n"'
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|
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# Format date
|
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perl -MPOSIX -e 'print strftime("%Y-%m-%d %H:%M:%S\n", localtime)'
|
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# Days between dates
|
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perl -MTime::Piece -e '$t1 = Time::Piece->strptime("2024-01-01", "%Y-%m-%d"); $t2 = Time::Piece->strptime("2024-12-31", "%Y-%m-%d"); print int(($t2 - $t1) / 86400), "\n"'
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# Convert epoch to date
|
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perl -e 'print scalar localtime(1704067200), "\n"'
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# Add days to date
|
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perl -MTime::Piece -MTime::Seconds -e '$t = localtime; $t += ONE_DAY * 7; print $t->strftime("%Y-%m-%d\n")'
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|
||||
# File age in days
|
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perl -e 'print int(-M $ARGV[0]), "\n"' file.txt
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||||
|
||||
# Show files modified today
|
||||
perl -e 'print "$_\n" for grep {int(-M $_) == 0} glob("*")'
|
||||
```
|
||||
|
||||
## Mathematical Operations
|
||||
|
||||
```bash
|
||||
# Calculator
|
||||
perl -e 'print eval($ARGV[0]), "\n"' "2 + 2 * 3"
|
||||
|
||||
# Sum numbers from stdin
|
||||
perl -ne '$sum += $_; END {print "$sum\n"}'
|
||||
|
||||
# Generate random numbers
|
||||
perl -e 'print int(rand(100)), "\n" for 1..10'
|
||||
|
||||
# Factorial
|
||||
perl -e '$f = 1; $f *= $_ for 1..$ARGV[0]; print "$f\n"' 5
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||||
|
||||
# Prime numbers
|
||||
perl -e 'for $n (2..100) {$p = 1; $n % $_ or $p = 0 for 2..sqrt($n); print "$n " if $p}'
|
||||
|
||||
# Fibonacci sequence
|
||||
perl -e '$a = $b = 1; print "$a "; for (1..20) {print "$b "; ($a, $b) = ($b, $a + $b)}'
|
||||
|
||||
# Convert hex to decimal
|
||||
perl -e 'print hex($ARGV[0]), "\n"' FF
|
||||
|
||||
# Convert decimal to hex
|
||||
perl -e 'printf "%X\n", $ARGV[0]' 255
|
||||
|
||||
# Convert binary to decimal
|
||||
perl -e 'print oct("0b" . $ARGV[0]), "\n"' 11111111
|
||||
|
||||
# Statistics
|
||||
perl -ne 'push @v, $_; END {$sum += $_ for @v; $avg = $sum/@v; $var += ($_-$avg)**2 for @v; print "Mean: $avg, StdDev: ", sqrt($var/@v), "\n"}' numbers.txt
|
||||
```
|
||||
|
||||
## Encoding and Conversion
|
||||
|
||||
```bash
|
||||
# Convert to uppercase
|
||||
perl -pe '$_ = uc'
|
||||
|
||||
# Convert to lowercase
|
||||
perl -pe '$_ = lc'
|
||||
|
||||
# Title case
|
||||
perl -pe 's/\b(\w)/\u$1/g'
|
||||
|
||||
# ROT13 encoding
|
||||
perl -pe 'tr/A-Za-z/N-ZA-Mn-za-m/'
|
||||
|
||||
# Convert ASCII to hex
|
||||
perl -ne 'print unpack("H*", $_), "\n"'
|
||||
|
||||
# Convert hex to ASCII
|
||||
perl -ne 'print pack("H*", $_)'
|
||||
|
||||
# Unicode operations
|
||||
perl -CS -pe 's/\N{U+00E9}/e/g' # Replace é with e
|
||||
|
||||
# Convert encoding
|
||||
perl -MEncode -pe '$_ = encode("UTF-8", decode("ISO-8859-1", $_))'
|
||||
```
|
||||
|
||||
## Quick Utilities
|
||||
|
||||
```bash
|
||||
# Generate UUID
|
||||
perl -MData::UUID -e 'print Data::UUID->new->create_str, "\n"'
|
||||
|
||||
# Password generator
|
||||
perl -e 'print map {("a".."z","A".."Z",0..9)[rand 62]} 1..16; print "\n"'
|
||||
|
||||
# Check if port is open
|
||||
perl -MIO::Socket::INET -e 'print IO::Socket::INET->new("$ARGV[0]:$ARGV[1]") ? "Open\n" : "Closed\n"' hostname 80
|
||||
|
||||
# Simple HTTP GET
|
||||
perl -MLWP::Simple -e 'print get($ARGV[0])' 'http://example.com'
|
||||
|
||||
# Send email
|
||||
perl -MMIME::Lite -e 'MIME::Lite->new(From => "sender@example.com", To => "recipient@example.com", Subject => "Test", Data => "Hello")->send'
|
||||
|
||||
# Benchmark code
|
||||
perl -MBenchmark -e 'timethis(1000000, sub {$x = 1 + 1})'
|
||||
|
||||
# Create tar archive
|
||||
perl -MArchive::Tar -e 'Archive::Tar->create_archive("archive.tar.gz", COMPRESS_GZIP, glob("*.txt"))'
|
||||
|
||||
# Weather (requires Internet)
|
||||
perl -MLWP::Simple -e 'print +(get("http://wttr.in/?format=3") =~ /: (.+)/)[0], "\n"'
|
||||
|
||||
# QR code generator
|
||||
perl -MImager::QRCode -e 'Imager::QRCode->new->plot($ARGV[0])->write(file => "qr.png")' "Hello World"
|
||||
|
||||
# Simple web server
|
||||
perl -MIO::All -e 'io(":8080")->fork->accept->(sub {$_[0] < io("index.html")})'
|
||||
|
||||
# Watch file for changes
|
||||
perl -e 'while (1) {$new = -M $ARGV[0]; print "Changed\n" if $new != $old; $old = $new; sleep 1}' file.txt
|
||||
|
||||
# Bulk email validator
|
||||
perl -MEmail::Valid -ne 'chomp; print "$_\n" if Email::Valid->address($_)' emails.txt
|
||||
|
||||
# Simple port scanner
|
||||
perl -MIO::Socket::INET -e 'for (1..1024) {print "$_\n" if IO::Socket::INET->new("$ARGV[0]:$_")}' hostname
|
||||
|
||||
# Directory tree
|
||||
perl -MFile::Find -e 'find(sub {$d = $File::Find::dir =~ tr!/!!; print " " x $d, "$_\n"}, ".")'
|
||||
```
|
||||
|
||||
## Performance One-Liners
|
||||
|
||||
```bash
|
||||
# Profile code execution
|
||||
perl -d:NYTProf -e 'your_code_here'
|
||||
|
||||
# Memory usage
|
||||
perl -e 'system("ps -o pid,vsz,rss,comm -p $$")'
|
||||
|
||||
# Time execution
|
||||
perl -MTime::HiRes=time -e '$t = time; system($ARGV[0]); printf "%.3f seconds\n", time - $t' "command"
|
||||
|
||||
# Count module load time
|
||||
perl -MTime::HiRes=time -e '$t = time; require Some::Module; printf "%.3f seconds\n", time - $t'
|
||||
```
|
||||
|
||||
## Tips for Writing One-Liners
|
||||
|
||||
1. **Essential Options**
|
||||
- `-e`: Execute code
|
||||
- `-n`: Loop over input lines (while (<>) {...})
|
||||
- `-p`: Loop and print (while (<>) {...; print})
|
||||
- `-i`: In-place editing
|
||||
- `-l`: Auto chomp and add newlines
|
||||
- `-a`: Auto-split into @F
|
||||
- `-F`: Set field separator for -a
|
||||
|
||||
2. **Special Variables**
|
||||
- `$_`: Current line/topic
|
||||
- `$.`: Line number
|
||||
- `@F`: Fields (with -a)
|
||||
- `$/`: Input record separator
|
||||
- `$\`: Output record separator
|
||||
|
||||
3. **Module Loading**
|
||||
- `-M`: Load module (-MJSON::PP)
|
||||
- `-m`: Load module without importing
|
||||
|
||||
4. **Common Patterns**
|
||||
- `BEGIN {}`: Run before loop
|
||||
- `END {}`: Run after loop
|
||||
- `next if`: Skip lines
|
||||
- `last if`: Stop processing
|
||||
|
||||
Remember: One-liners are powerful but can become unreadable. If a one-liner grows too complex, consider writing a proper script. The goal is efficiency, not obscurity.
|
||||
|
||||
*"The best one-liner is the one that gets the job done and is still understandable tomorrow."*
|
||||
Reference in New Issue
Block a user