Visit Jeremy's Blog.
Go Back > Forums > Linux Forums > Linux - General
User Name
Linux - General This Linux forum is for general Linux questions and discussion.
If it is Linux Related and doesn't seem to fit in any other forum then this is the place.


  Search this Thread
Old 11-19-2009, 09:34 PM   #1
Registered: Jun 2008
Posts: 31

Rep: Reputation: 16
/dev/fd question

what exactly is going on in this piece of code? what is the role of /dev/fd? i know that /dev/fd/0 is somehow linked to standard input, but that's the extent of my knowledge

cat header.txt /dev/fd/0 footer.txt
Old 11-19-2009, 10:56 PM   #2
LQ Guru
Registered: Dec 2006
Location: underground
Distribution: Slackware64
Posts: 7,594

Rep: Reputation: 551Reputation: 551Reputation: 551Reputation: 551Reputation: 551Reputation: 551

The above link explains /dev/fd. Generally /dev/fd/ has an entry for stdin, stdout, and stderr. stdin is /dev/fd/0.

Therefore, your code cats a file called header.txt, followed by stdin, followed by the file footer.txt, one after the other. It is the equivalent to:

cat header.txt - footer.txt

where the dash in the middle signifies stdin.

Old 11-20-2009, 12:54 AM   #3
Registered: Jun 2008
Posts: 31

Original Poster
Rep: Reputation: 16
the explanation in the link is almost exactly the same as the one given in the manual i'm reading. i'm afraid i still don't understand it.
Old 11-20-2009, 02:48 AM   #4
Registered: Jun 2008
Posts: 31

Original Poster
Rep: Reputation: 16
ok i think i have the /dev/fd/0 figured out. i have another question, still related to re-direction. what's the difference with:

exec 7<&0

exec 7>&0


input, io, output, redirection

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
pseudo terminals: /dev/ptmx <-> /dev/pts/ vs. /dev/ptyp <-> /dev/ttyp rtspitz Linux - Software 2 12-02-2011 03:07 PM
[SOLVED] wiping HDD using /dev/urandom versus /dev/zero, a theoretical question H_TeXMeX_H Linux - General 6 06-29-2009 07:55 AM
OpenSUSE x86_64 does not mount /dev/tape (or /dev/st0 or /dev/nst0) yankeeinga Linux - Newbie 6 08-21-2008 01:51 PM
using flash drive changes device /dev/sr0 to /dev/sr1 for mapping to /dev/pktcdvd/0? lugoteehalt Linux - Software 3 10-24-2007 11:27 AM
Clone with dd if=/dev/hda of=/dev/hdb question wrc1944 Linux - Hardware 2 11-28-2004 10:10 AM > Forums > Linux Forums > Linux - General

All times are GMT -5. The time now is 06:15 PM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration