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Full Discussion: Purpose of <>
Top Forums UNIX for Dummies Questions & Answers Purpose of <> Post 302607538 by drl on Wednesday 14th of March 2012 05:04:42 PM
Old 03-14-2012
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;
 

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env(1)								   User Commands							    env(1)

NAME
env - set environment for command invocation SYNOPSIS
/usr/bin/env [-i | -] [name=value]... [utility [arg... ]] /usr/xpg4/bin/env [-i | -] [name=value]... [utility [arg... ]] DESCRIPTION
The env utility obtains the current environment, modifies it according to its arguments, then invokes the utility named by the utility op- erand with the modified environment. Optional arguments are passed to utility. If no utility operand is specified, the resulting environment is written to the standard output, with one name=value pair per line. /usr/bin If env executes commands with arguments, it uses the default shell /usr/bin/sh (see sh(1)). /usr/xpg4/bin If env executes commands with arguments, it uses /usr/xpg4/bin/sh (see ksh(1)). OPTIONS
The following options are supported: -i | - Ignores the environment that would otherwise be inherited from the current shell. Restricts the environment for utility to that specified by the arguments. OPERANDS
The following operands are supported: name=value Arguments of the form name=value modify the execution environment, and are placed into the inherited environment before utility is invoked. utility The name of the utility to be invoked. If utility names any of the special shell built-in utilities, the results are unde- fined. arg A string to pass as an argument for the invoked utility. EXAMPLES
Example 1 Invoking utilities with new PATH values The following utility: example% env -i PATH=/mybin mygrep xyz myfile invokes the utility mygrep with a new PATH value as the only entry in its environment. In this case, PATH is used to locate mygrep, which then must reside in /mybin. ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of env: LANG, LC_ALL, LC_CTYPE, LC_MES- SAGES, and NLSPATH. PATH Determine the location of the utility. If PATH is specified as a name=value operand to env, the value given shall be used in the search for utility. EXIT STATUS
If utility is invoked, the exit status of env is the exit status of utility. Otherwise, the env utility returns one of the following exit values: 0 Successful completion. 1-125 An error occurred. 126 utility was found but could not be invoked. 127 utility could not be found. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: /usr/bin +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |CSI |enabled | +-----------------------------+-----------------------------+ /usr/xpg4/bin +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWxcu4 | +-----------------------------+-----------------------------+ |CSI |enabled | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
ksh(1), sh(1), exec(2), profile(4), attributes(5), environ(5), standards(5) SunOS 5.11 2 Jan 2002 env(1)
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