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Mike Schilli


Sysadm::Install - Typical installation tasks for system administrators


  use Sysadm::Install qw(:all);

  my $INST_DIR = '/home/me/install/';

  cp("/deliver/someproj.tgz", ".");

     # Write out ...
  blurt("Builder: Mike\nDate: Today\n", "build.dat");

     # Slurp back in ...
  my $data = slurp("build.dat");

     # or edit in place ...
  pie(sub { s/Today/scalar localtime()/ge; $_; }, "build.dat");

  make("test install");

     # run a cmd and tap into stdout and stderr
  my($stdout, $stderr, $exit_code) = tap("ls", "-R");


Have you ever wished for your installation shell scripts to run reproducibly, without much programming fuzz, and even with optional logging enabled? Then give up shell programming, use Perl.

Sysadm::Install executes shell-like commands performing typical installation tasks: Copying files, extracting tarballs, calling make. It has a fail once and die policy, meticulously checking the result of every operation and calling die() immediately if anything fails.

Sysadm::Install also supports a dry_run mode, in which it logs everything, but suppresses any write actions. Dry run mode is enabled by calling Sysadm::Install::dry_run(1). To switch back to normal, call Sysadm::Install::dry_run(0).

As of version 0.17, Sysadm::Install supports a confirm mode, in which it interactively asks the user before running any of its functions (just like rm -i). confirm mode is enabled by calling Sysadm::Install::confirm(1). To switch back to normal, call Sysadm::Install::confirm(0).

Sysadm::Install is fully Log4perl-enabled. To start logging, just initialize Log::Log4perl. Sysadm::Install acts as a wrapper class, meaning that file names and line numbers are reported from the calling program's point of view.


cp($source, $target)

Copy a file from $source to $target. target can be a directory. Note that cp doesn't copy file permissions. If you want the target file to reflect the source file's user rights, use perm_cp() shown below.

mv($source, $target)

Move a file from $source to $target. target can be a directory.


Download a file specified by $url and store it under the name returned by basename($url).


Untar the tarball in $tarball, which typically adheres to the someproject-X.XX.tgz convention. But regardless of whether the archive actually contains a top directory someproject-X.XX, this function will behave if it had one. If it doesn't have one, a new directory is created before the unpacking takes place. Unpacks the tarball into the current directory, no matter where the tarfile is located. Please note that if you're using a compressed tarball (.tar.gz or .tgz), you'll need IO::Zlib installed.

untar_in($tar_file, $dir)

Untar the tarball in $tgz_file in directory $dir. Create $dir if it doesn't exist yet.

pick($prompt, $options, $default, $opts)

Ask the user to pick an item from a displayed list. $prompt is the text displayed, $options is a referenc to an array of choices, and $default is the number (starting from 1, not 0) of the default item. For example,

    pick("Pick a fruit", ["apple", "pear", "pineapple"], 3);

will display the following:

    [1] apple
    [2] pear
    [3] pineapple
    Pick a fruit [3]>

If the user just hits Enter, "pineapple" (the default value) will be returned. Note that 3 marks the 3rd element of the list, and is not an index value into the array.

If the user enters 1, 2 or 3, the corresponding text string ("apple", "pear", "pineapple" will be returned by pick().

If the optional $opts hash has { tty => 1 } set, then the user reponse will be expected from the console, not STDIN.

ask($prompt, $default, $opts)

Ask the user to either hit Enter and select the displayed default or to type in another string.

If the optional $opts hash has { tty => 1 } set, then the user reponse will be expected from the console, not STDIN.


Create a directory of arbitrary depth, just like File::Path::mkpath.


Delete a directory and all of its descendents, just like rm -rf in the shell.


chdir to the given directory. If you don't want to have cd() modify the internal directory stack (used for subsequent cdback() calls), set the stack_update parameter to a false value:

    cd($dir, {stack_update => 0});

chdir back to the last directory before a previous cd. If the option reset is set, it goes all the way back to the beginning of the directory stack, i.e. no matter how many cd() calls were made in between, it'll go back to the original directory:

      # go all the way back
    cdback( { reset => 1 } );

Call make in the shell.

pie($coderef, $filename, ...)

Simulate "perl -pie 'do something' file". Edits files in-place. Expects a reference to a subroutine as its first argument. It will read out the file $filename line by line and calls the subroutine setting a localized $_ to the current line. The return value of the subroutine will replace the previous value of the line.


    # Replace all 'foo's by 'bar' in test.dat
        pie(sub { s/foo/bar/g; $_; }, "test.dat");

Works with one or more file names.

If the files are known to contain UTF-8 encoded data, and you want it to be read/written as a Unicode strings, use the utf8 option:

    pie(sub { s/foo/bar/g; $_; }, "test.dat", { utf8 => 1 });
plough($coderef, $filename, ...)

Simulate "perl -ne 'do something' file". Iterates over all lines of all input files and calls the subroutine provided as the first argument.


    # Print all lines containing 'foobar'
        plough(sub { print if /foobar/ }, "test.dat");

Works with one or more file names.

If the files are known to contain UTF-8 encoded data, and you want it to be read into Unicode strings, use the utf8 option:

    plough(sub { print if /foobar/ }, "test.dat", { utf8 => 1 });
my $data = slurp($file, $options)

Slurps in the file and returns a scalar with the file's content. If called without argument, data is slurped from STDIN or from any files provided on the command line (like <> operates).

If the file is known to contain UTF-8 encoded data and you want to read it in as a Unicode string, use the utf8 option:

    my $unicode_string = slurp( $file, {utf8 => 1} );
blurt($data, $file, $append)

Opens a new file, prints the data in $data to it and closes the file. If $append is set to a true value, data will be appended to the file. Default is false, existing files will be overwritten.

If the string is a Unicode string, use the utf8 option:

    blurt( $unicode_string, $file, {utf8 => 1} );
blurt_atomic($data, $file, $options)

Write the data in $data to a file $file, guaranteeing that the operation will either complete fully or not at all. This is accomplished by first writing to a temporary file which is then rename()ed to the target file.

Unlike in blurt, there is no $append mode in blurt_atomic.

If the string is a Unicode string, use the utf8 option:

    blurt_atomic( $unicode_string, $file, {utf8 => 1} );
($stdout, $stderr, $exit_code) = tap($cmd, @args)

Run a command $cmd in the shell, and pass it @args as args. Capture STDOUT and STDERR, and return them as strings. If $exit_code is 0, the command succeeded. If it is different, the command failed and $exit_code holds its exit code.

Please note that tap() is limited to single shell commands, it won't work with output redirectors (ls >/tmp/foo 2>&1).

In default mode, tap() will concatenate the command and args given and create a shell command line by redirecting STDERR to a temporary file. tap("ls", "/tmp"), for example, will result in

    'ls' '/tmp' 2>/tmp/sometempfile |

Note that all commands are protected by single quotes to make sure arguments containing spaces are processed as singles, and no globbing happens on wildcards. Arguments containing single quotes or backslashes are escaped properly.

If quoting is undesirable, tap() accepts an option hash as its first parameter,

    tap({no_quotes => 1}, "ls", "/tmp/*");

which will suppress any quoting:

    ls /tmp/* 2>/tmp/sometempfile |

Or, if you prefer double quotes, use

    tap({double_quotes => 1}, "ls", "/tmp/$VAR");

wrapping all args so that shell variables are interpolated properly:

    "ls" "/tmp/$VAR" 2>/tmp/sometempfile |

Another option is "utf8" which runs the command in a terminal set to UTF8.

Error handling: By default, tap() won't raise an error if the command's return code is nonzero, indicating an error reported by the shell. If bailing out on errors is requested to avoid return code checking by the script, use the raise_error option:

    tap({raise_error => 1}, "ls", "doesn't exist");

In DEBUG mode, tap logs the entire stdout/stderr output, which can get too verbose at times. To limit the number of bytes logged, use the stdout_limit and stderr_limit options

    tap({stdout_limit => 10}, "echo", "123456789101112");
$quoted_string = qquote($string, [$metachars])

Put a string in double quotes and escape all sensitive characters so there's no unwanted interpolation. E.g., if you have something like

   print "foo!\n";

and want to put it into a double-quoted string, it will look like

    "print \"foo!\\n\""

Sometimes, not only backslashes and double quotes need to be escaped, but also the target environment's meta chars. A string containing

    print "$<\n";

needs to have the '$' escaped like

    "print \"\$<\\n\";"

if you want to reuse it later in a shell context:

    $ perl -le "print \"\$<\\n\";"

qquote() supports escaping these extra characters with its second, optional argument, consisting of a string listing all escapable characters:

    my $script  = 'print "$< rocks!\\n";';
    my $escaped = qquote($script, '!$'); # Escape for shell use
    system("perl -e $escaped");

    => 1212 rocks!

And there's a shortcut for shells: By specifying ':shell' as the metacharacters string, qquote() will actually use '!$`'.

For example, if you wanted to run the perl code

    print "foobar\n";


    perl -e ...

on a box via ssh, you would use

    use Sysadm::Install qw(qquote);

    my $cmd = 'print "foobar!\n"';
       $cmd = "perl -e " . qquote($cmd, ':shell');
       $cmd = "ssh somehost " . qquote($cmd, ':shell');

    print "$cmd\n";

and get

    ssh somehost "perl -e \"print \\\"foobar\\\!\\\\n\\\"\""

which runs on somehost without hickup and prints foobar!.

Sysadm::Install comes with a script one-liner (installed in bin), which takes arbitrary perl code on STDIN and transforms it into a one-liner:

    $ one-liner
    Type perl code, terminate by CTRL-D
    print "hello\n";
    print "world\n";
    perl -e "print \"hello\\n\"; print \"world\\n\"; "
$quoted_string = quote($string, [$metachars])

Similar to qquote(), just puts a string in single quotes and escapes what needs to be escaped.

Note that shells typically don't support escaped single quotes within single quotes, which means that

    $ echo 'foo\'bar'

is invalid and the shell waits until it finds a closing quote. Instead, there is an evil trick which gives the desired result:

    $ echo 'foo'\''bar'  # foo, single quote, \, 2 x single quote, bar

It uses the fact that shells interpret back-to-back strings as one. The construct above consists of three back-to-back strings:

    (1) 'foo'
    (2) '
    (3) 'bar'

which all get concatenated to a single


If you call quote() with $metachars set to ":shell", it will perform that magic behind the scenes:

    print quote("foo'bar");
      # prints: 'foo'\''bar'
perm_cp($src, $dst, ...)

Read the $src file's user permissions and modify all $dst files to reflect the same permissions.

owner_cp($src, $dst, ...)

Read the $src file/directory's owner uid and group gid and apply it to $dst.

For example: copy uid/gid of the containing directory to a file therein:

    use File::Basename;

    owner_cp( dirname($file), $file );

Usually requires root privileges, just like chown does.

$perms = perm_get($filename)

Read the $filename's user permissions and owner/group. Returns an array ref to be used later when calling perm_set($filename, $perms).

perm_set($filename, $perms)

Set file permissions and owner of $filename according to $perms, which was previously acquired by calling perm_get($filename).


Run a shell command via system() and die() if it fails. Also works with a list of arguments, which are then interpreted as program name plus arguments, just like system() does it.

hammer($cmd, $arg, ...)

Run a command in the shell and simulate a user hammering the ENTER key to accept defaults on prompts.

say($text, ...)

Alias for print ..., "\n", just like Perl6 is going to provide it.


Check if the current script is running as root. If yes, continue. If not, restart the current script with all command line arguments is restarted under sudo:

    sudo scriptname args ...

Make sure to call this before any @ARGV-modifying functions like getopts() have kicked in.


Search all directories in $PATH (the ENV variable) for an executable named $program and return the full path of the first hit. Returns undef if the program can't be found.


Opens a file handle to read the output of the following process:

    cd $dir; find ./ -xdev -print0 | cpio -o0 |

This can be used to capture a file system structure.


Opens a file handle to write to a

    | (cd $dir; cpio -i0)

process to restore a file system structure. To be used in conjunction with fs_read_open.

pipe_copy($in, $out, [$bufsize])

Reads from $in and writes to $out, using sysread and syswrite. The buffer size used defaults to 4096, but can be set explicitely.

snip($data, $maxlen)

Format the data string in $data so that it's only (roughly) $maxlen characters long and only contains printable characters.

If $data is longer than $maxlen, it will be formatted like


indicating the length of the original string, the beginning, the end, and the number of 'snipped' characters.

If $data is shorter than $maxlen, it will be returned unmodified (except for unprintable characters replaced, see below).

If $data contains unprintable character's they are replaced by "." (the dot).


Reads in a password to be typed in by the user in noecho mode. A call to password_read("password: ") results in

    password: ***** (stars aren't actually displayed)

This function will switch the terminal back into normal mode after the user hits the 'Return' key.


Format the time in a human-readable way, less wasteful than the 'scalar localtime' formatting.

    print nice_time(), "\n";
      # 2007/04/01 10:51:24

It uses the system time by default, but it can also accept epoch seconds:

    print nice_time(1170000000), "\n";
      # 2007/01/28 08:00:00

It uses localtime() under the hood, so the outcome of the above will depend on your local time zone setting.

def_or($foo, $default)

Perl-5.9 added the //= construct, which helps assigning values to undefined variables. Instead of writing

    if(!defined $foo) {
        $foo = $default;

you can just write

    $foo //= $default;

However, this is not available on older perl versions (although there's source filter solutions). Often, people use

    $foo ||= $default;

instead which is wrong if $foo contains a value that evaluates as false. So Sysadm::Install, the everything-and-the-kitchen-sink under the CPAN modules, provides the function def_or() which can be used like

    def_or($foo, $default); 

to accomplish the same as

    $foo //= $default;

How does it work, how does $foo get a different value, although it's apparently passed in by value? Modifying $_[0] within the subroutine is an old Perl trick to do exactly that.


Check if the given string has the utf8 flag turned on. Works just like Encode.pm's is_utf8() function, except that it silently returns a false if Encode isn't available, for example when an ancient perl without proper utf8 support is used.


Check if we're using a perl with proper utf8 support, by verifying the Encode.pm module is available for loading.


Return the path to the home directory of the current user.


Mike Schilli, <m@perlmeister.com>


Copyright (C) 2004-2007 by Mike Schilli

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.3 or, at your option, any later version of Perl 5 you may have available.