If that were even valid, what would it accomplish? The instant you open a file with >, you truncate it, leaving nothing to read.
I have used similar syntax used in bash to open device files:
Code:
exec 5<>/dev/ttyUSB1
...to open a serial port for instance. Then I could echo asdf >&5 and read <&5 without reopening and re-closing the serial port every call. But I believe that's BASH-only syntax, and only useful in very specific circumstances.
Last edited by Corona688; 03-14-2012 at 01:13 PM..
Location: Saint Paul, MN USA / BSD, CentOS, Debian, OS X, Solaris
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Hi.
The <> re-direction operator is also available in ksh and zsh.
The serial port example makes it useful ... cheers, drl
---------- Post updated at 12:48 ---------- Previous update was at 12:27 ----------
Hi.
Associating a file descriptor with an existing file does not destroy it:
Code:
#!/usr/bin/env bash
# @(#) s3 Demonstrate <> re-direction operator.
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && . $C
echo first time > f
pl " Initial content of file f:"
cat f
pl " Associate descriptor 4 with file f, show file:"
exec 4<>f
cat f
ls -lgG f
read -u 4 line
pe " variable line read from FD 4 as \"$line\""
pl " Write to f:"
echo hi >f
ls -lgG f
pl " Read from f:"
cat <f
exit 0
producing:
Code:
% ./s3
Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution : Debian GNU/Linux 5.0.8 (lenny)
bash GNU bash 3.2.39
-----
Initial content of file f:
first time
-----
Associate descriptor 4 with file f, show file:
first time
-rw-r--r-- 1 11 Mar 14 12:46 f
variable line read from FD 4 as "first time"
-----
Write to f:
-rw-r--r-- 1 3 Mar 14 12:46 f
-----
Read from f:
hi
Location: Saint Paul, MN USA / BSD, CentOS, Debian, OS X, Solaris
Posts: 2,288
Thanks Given: 430
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Hi.
The construct <>filename seems to work with ksh:
Code:
#!/usr/bin/env ksh
#!/usr/bin/env zsh
#!/usr/bin/env bash
# @(#) s4 Demonstrate <> re-direction operator.
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && . $C
echo first time > f
pl " Initial content of file f:"
cat f
pl " Associate descriptor with file f, show file:"
# exec 4<>f
<>f
cat f
ls -lgG f
read -u 0 line
pe " variable line read from FD as \"$line\""
pl " Write to f:"
echo hi >f
ls -lgG f
pl " Read from f:"
cat <f
exit 0
producing:
Code:
./s4
Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.32-5-686, i686
Distribution : Debian GNU/Linux 6.0.3 (squeeze)
ksh 93s+
-----
Initial content of file f:
first time
-----
Associate descriptor with file f, show file:
first time
-rw-r----- 1 11 Mar 14 16:00 f
xx
variable line read from FD as "xx"
-----
Write to f:
-rw-r----- 1 3 Mar 14 16:00 f
-----
Read from f:
hi
I needed to enter something from the keyboard for the read -u. So the intent seems OK, but perhaps a problem with bash ... cheers, dr;
Hi,
Anyone, please explain the purpose of /dev/ipldevice in AIX .. it would be a problem if there is no /dev/ipldevice while booting.
Regards,
Siva (1 Reply)
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Hi All
Can anybody tell me what is the purpose of inv in the below command.
ftp -inv $RFTPSERVER /temp/te.txt << EOF
and << its stands for what..
Thanks (1 Reply)
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nohup ./append_import.sh 1 > import1.out 2>&1 < /dev/null &
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whats the purpose of the following script? who could run it? To what is the script refering that exceeds 75%? The mailbox?
What does sed 's/%//' do? (1 Reply)
03-14-2012
