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71 lines
2.8 KiB
Plaintext
71 lines
2.8 KiB
Plaintext
# perl
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# The Perl 5 language interpreter.
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# Parse and execute a Perl script:
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perl script.pl
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# Check syntax errors on a Perl script:
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perl -c script.pl
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# Parse and execute a perl statement:
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perl -e perl_statement
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# Import module before execution of a perl statement:
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perl -Mmodule -e perl_statement
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# Run a Perl script in debug mode, using perldebug:
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perl -d script.pl
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# Loo[p] over all lines of a file, editing them [i]n-place
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# using a find/replace [e]xpression
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perl -p -i -e 's/find/replace/g' filename
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# Run a find/replace expression on a file,
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# saving the original file with a given extension:
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perl -p -i'.old' -e 's/find/replace/g' filename
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# See also:
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# Perl language cheat sheets at /perl/
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# list of pages: /perl/:list
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# learn perl: /perl/:learn
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# perl one-liners: /perl/1line
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# search in pages: /perl/~keyword
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# Perl method of listing out the environment variables, sans values.
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perl -e 'print("$_\n") foreach keys(%ENV)'
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# Output the columns and lines of the current terminal.
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perl -e 'use Term::ReadKey "GetTerminalSize"; my ($Cols, $Lines) = GetTerminalSize(); print("${Cols}x$Lines\n")'
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# List out all of the aliases within the provided file. This works by iterating
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# over each line of the file, displaying only those lines matching the REGEX.
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# Before printing out the relevant lines, all tabs are removed.
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perl -ne '/^[[:space:]]+alias/ and print(tr/\t//dr)' "$HOME/.bash_aliases"
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# Alternative logic approach:
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perl -ne 'print(tr/\t//dr) if /^[[:space:]]+alias/' "$HOME/.bash_aliases"
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# See if the current user has a non-empty password value. This may not work for
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# systems set up with shadow passwords, however.
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perl -ne '/^$ARGV[0]::$</ and print(STDERR "WARNING: User has an empty password.\n")' /etc/passwd ichy
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# Display the current user's UID and GID in a format ideal for chmod(1).
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perl -e 'print("$<:" . (split(" ", $)))[0] . "\n")'
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# Permissions allowing, output the first 512 bytes of an MBR storage device, -
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# where the partition table should be stored, using Perl's read() function.
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#
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# Note that the 2-argument style open() should not be used unless the file is
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# static; no chance of changing to something potentially problematic.
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#
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# You might spot some printable strings, such as 'LILO' or 'GRUB', if you've
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# also stored your bootloader on the MBR of the storage device (non-UEFI).
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perl -e 'open(my $FH, "</dev/sda"); read($FH, my $Data, 512); close($FH); print("$Data\n")'
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# Create a simple table of users within your system. This example demonstrates
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# the use of the `getpwent()` subroutine, which, upon each execution, holds an
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# array of each field in each line within the '/etc/passwd' file.
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printf("%-15s %-5s %-5s %-s\n", 'USERNAME', 'UID', 'GID', 'HOME');
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while (my @Data = getpwent()) {
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printf("%-15s %-5s %-5s %-s\n", $Data[0], $Data[2], $Data[3], $Data[7])
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}
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