adding non printable characters in perl's print function

jesuashok has asked for the wisdom of the Perl Monks concerning the following question:

fellow monks,

#!/usr/bin/perl

use strict;

print ":Hello ^M world:\n";
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Output :-

 World:
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In the above code, I typed "Hello World" as follows :-

Hello <ctrl+v><ctrl+m>world
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Could any one explain me the output which I got ?

Comment on adding non printable characters in perl's print function Select or Download Code

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Re: adding non printable characters in perl's print function by ikegami (Patriarch) on Feb 21, 2007 at 06:36 UTC
Character 13, in ASCII and derived character sets, is Carriage Return (CR). It is a non-printable character that terminals usually interpret as a request to move the cursor to the start of the current line. It can be represented as `\r` (at least on Windows and unix systems), `\x0D` and `\015` in Perl string literals to avoid the trouble of actually placing the character in the literal. Some fun with `\r`: `$\| = 1; # Turn off buffering on STDOUT. print( " 5"); sleep(1); print("\r 4"); sleep(1); print("\r 3"); sleep(1); print("\r 2"); sleep(1); print("\r 1"); sleep(1); print("\r BOOM \n");` [download]	[reply] [d/l] [select]
Re^2: adding non printable characters in perl's print function by Anno (Deacon) on Feb 21, 2007 at 19:30 UTC
`printf( "\r%5s", $_), sleep( /\d/) for reverse "\r BOOM \n", 1 .. 5; # :)` Anno	[reply] [d/l]
Re^3: adding non printable characters in perl's print function by ikegami (Patriarch) on Feb 21, 2007 at 19:35 UTC
The purpose of the snippet was to highlight the effect of `\r`, not to hide it.	[reply] [d/l]
Re^4: adding non printable characters in perl's print function by Anno (Deacon) on Feb 21, 2007 at 19:53 UTC
Re: adding non printable characters in perl's print function by Zaxo (Archbishop) on Feb 21, 2007 at 06:29 UTC
Control-M is carriage return without linefeed. ":Hello " is printed, then the print position returns to the start of the line and "World:" overwrites it. That is often used for text-mode progress counters and spinners. After Compline, Zaxo	[reply]
Re: adding non printable characters in perl's print function by redlemon (Hermit) on Feb 21, 2007 at 10:20 UTC
A quick way to check your output to see everything you put in comes out is to use the 'od' command (on any unix-like box): `perl -e 'print ":Hello ^M world:\n"' \| od -c` This will give you `0000000 : H e l l o \r w o r l d : \n` -- Lyon	[reply] [d/l] [select]
Re: adding non printable characters in perl's print function by dsheroh (Monsignor) on Feb 21, 2007 at 16:07 UTC
To answer the implicit half of your question, to get the effect of `\n` you need both a carriage return (to go to the start of the line) and a line feed (to go to the next line). This combination is frequently referred to as a "CRLF". `#!/usr/bin/perl use strict; print ":Hello \x0D\x0A world:\n";` [download] This outputs `:Hello world:` [download] Note that this is all a bit system-dependent, as `\n` represents only a LF on Unix-type systems (which add an implicit CR), only a CR on (pre-OS X) Macs (which add an implicit LF), and CRLF on Windows. So it's probably best to just use `\n` instead of mucking about with the literal control characters anyhow.	[reply] [d/l] [select]