03-18-2003
PERL: how to tell if variable is NULL
How to I do a check on a variable to see if it's null-- I am using Perl.
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I have the necessity to use this command:
cat file1 | grep $A | grep $B
where sometime A and, or, B are not set.
For example:
I set A=@
never defined or set B
The above command send a cat error.
Any idea?
Thanks.
Giovanni (1 Reply)
Discussion started by: gio123bg
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Hello
I want to check for NULL variable..
but this is not working..please help
thanks in advance
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hi forum
i beginning with script and i want test un null variable in a schell
i just don t know the syntax here is a litle example
y=test
echo $y
unset y
echo $y (so here Y = Null)
if Y=Null
then
echo "y is null"
exit
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Hi,
I have to check whether an argument say $ARGV is not null in an if operator. Please let me know the operator. It would be great if you write a psuedo code.
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korn shell
If
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sample.cfg
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UPDATE=`cat $logfile1 | egrep -i "Update" | sed 's/ */ /g' | cut -d" " -f2`
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sh(1) General Commands Manual sh(1)
NAME
sh - Shell, the standard command language interpreter
DESCRIPTION
[Tru64 UNIX] Tru64 UNIX provides two command interpreters with the name sh. The XCU5.0 and POSIX.2 compliant command interpreter sh is
available in the file /usr/bin/posix/sh and is described in the sh(1p) reference page. The Bourne shell, historically known as sh, is
available in the file /usr/bin/sh and is described in the sh(1b) reference page.
[Tru64 UNIX] Your initial, or login, shell is determined by your entry in the file /etc/passwd. This file can be changed only by your sys-
tem administrator. You must use whatever procedures are in place at your location to have this entry changed.
[Tru64 UNIX] If available on your system, you may use the passwd -s or the chsh commands to change your login shell.
Note
This option is not available if your site manages passwords through the Network Information Service (NIS) facility. Check with your system
administrator.
[Tru64 UNIX] Subsequent shells spawned from the initial shell depend on the value in the environment variable BIN_SH. If this variable is
set to xpg4, the POSIX shell is started. If this variable is set to svr4, an SVR4 compliant version of the shell is started. If this vari-
able is unset, the Bourne shell is started. If this variable is set to any other value, an error is reported and the results are unpre-
dictable. See the EXAMPLES section for information on setting this variable.
NOTES
[Tru64 UNIX] With Tru64 UNIX Version 4.0 the Korn shell, /usr/bin/ksh is the same as the POSIX shell /usr/bin/posix/sh.
RESTRICTIONS
[Tru64 UNIX] The file /etc/shells must include entries for both the POSIX shell /usr/bin/posix/sh and the Bourne shell, /usr/bin/sh. If
this file is incorrect, see your system administrator.
EXAMPLES
Using the Bourne, Korn, or POSIX shell, to set the variable BIN_SH to use the POSIX/ XCU5.0compliant shell, enter: BIN_SH=xpg4 export
BIN_SH Using the Bourne, Korn, or POSIX shell, to set the variable BIN_SH to use the SVR4 compliant shell, enter: BIN_SH=svr4 export BIN_SH
Using the Bourne, Korn, or POSIX shell, to unset the variable BIN_SH, enter: unset BIN_SH Using the C/ shell, to set the variable BIN_SH to
use the POSIX/XCU5.0 compliant shell, enter: setenv BIN_SH xpg4 Using the C/ shell, to set the variable BIN_SH to use the SVR4 compliant
shell, enter: setenv BIN_SH svr4 Using the C/ shell, to unset the variable BIN_SH, enter: unsetenv BIN_SH
FILES
User profile. Contains user information, including the login shell name. Contains the names of available and permitted shells.
SEE ALSO
Commands: csh(1), ksh(1), Bourne shell sh(1b), POSIX shell sh(1p), passwd(1)
Files: passwd(4), shells(4)
Standards: standards(5)
sh(1)