Running operating system commands in Perl

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Perl is excellent "glueware" - a language which can be well used to connect together a whole lot of elements. And one of those elements may be operating system commands run from within the Perl program.

Here are (three!) ways that you can do it - in each case leaving the result of running the commands in a scalar variable.

# CAUTION - OS Dependent!

 

$imc = `uname -m`;

 

$imd = qx!uname -r!;

 

$imcalled = <<`DONE`

uname -s

date

uptime

DONE

;

 

# CAUTION - OS Dependent!

 

print ("***** Here document:\n$imcalled\n");

print ("***** Backquote:\n$imc\n");

print ("***** qx:\n$imd");

So that's
* A text string of commands in backquotes
* A text string of commands in a 'qx' string
* A text block (here document)

And here's how it runs:

BirthdayBoy:csr1 grahamellis$ perl bq

***** Here document:

Darwin

Tue  8 Jul 2008 18:41:38 BST

18:41  up 31 mins, 2 users, load averages: 0.01 0.05 0.06

 

***** Backquote:

Power Macintosh

 

***** qx:

9.0.0

BirthdayBoy:csr1 grahamellis$

You can also run operating system commands via a piped file handle, where you'll read back the response line by line:

open (FH,"ls -l *.*|");

while ($line = <FH>) {

  print ++$n," ",$line;

  }

Which gives us ...

BirthdayBoy:csr1 grahamellis$ perl lbl

1 -rw-r--r--  1 grahamellis  grahamellis  2856  7 Jul 16:35 dis.txt

2 -rw-r--r--  1 grahamellis  grahamellis   825  8 Jul 09:24 fred.txt

3 -rw-r--r--  1 grahamellis  grahamellis     3  7 Jul 10:04 pod2htmd.tmp

4 -rw-r--r--  1 grahamellis  grahamellis     3  7 Jul 10:04 pod2htmi.tmp

5 -rw-r--r--  1 grahamellis  grahamellis   502  8 Jul 14:28 tick.pm

BirthdayBoy:csr1 grahamellis$

(By the way - the name of my computer today - "BirthdayBoy" - has been allocated to me by the router at the hotel and does not imply anything about the day I was born!)
(written 2008-07-08, updated 2008-07-10)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

P258 - Perl - Solaris, OSX and Linux
  [1633] Changing a screen saver from a web page (PHP, Perl, OSX) - (2008-05-06)
  [2022] Pre and post increment - the ++ operator - (2009-02-03)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)

P214 - Perl - System Dependencies
  [733] Perl for Systems Admin - suid scripts - (2006-05-25)
  [2825] Perl course - is it tailored to Linux, or Microsoft Windows? - (2010-06-25)

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