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Full Discussion: How do I change a variable to something only if it's empty?
Top Forums Shell Programming and Scripting How do I change a variable to something only if it's empty? Post 302544419 by tukuyomi on Wednesday 3rd of August 2011 04:48:07 PM
Old 08-03-2011
What about this, maybe:
Code:
#!/bin/bash

hostname="network"
ip="192.168.1.1"
netmask=""

variables=( $hostname $ip $netmask  )

echo hostname: ${variables[0]:=--}
echo ip: ${variables[1]:=--}
echo netmask: ${variables[2]:=--}

exit 0

Or this, if you do not need the array:
Code:
#!/bin/sh

hostname="network"
ip="192.168.1.1"
netmask=""

echo hostname: ${hostname:=--}
echo ip: ${ip:=--}
echo netmask: ${netmask:=--}

exit 0

Last edited by tukuyomi; 08-03-2011 at 05:54 PM.. Reason: Added second code
 

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LEARN ABOUT MINIX

chsh

CHSH(1)                                                            User Commands                                                           CHSH(1)

NAME

       chsh - change login shell

SYNOPSIS

       chsh [options] [LOGIN]

DESCRIPTION

       The chsh command changes the user login shell. This determines the name of the user's initial login command. A normal user may only change
       the login shell for her own account; the superuser may change the login shell for any account.

OPTIONS

       The options which apply to the chsh command are:

       -h, --help
           Display help message and exit.

       -R, --root CHROOT_DIR
           Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.

       -s, --shell SHELL
           The name of the user's new login shell. Setting this field to blank causes the system to select the default login shell.

       If the -s option is not selected, chsh operates in an interactive fashion, prompting the user with the current login shell. Enter the new
       value to change the shell, or leave the line blank to use the current one. The current shell is displayed between a pair of [ ] marks.

NOTE

       The only restriction placed on the login shell is that the command name must be listed in /etc/shells, unless the invoker is the superuser,
       and then any value may be added. An account with a restricted login shell may not change her login shell. For this reason, placing /bin/rsh
       in /etc/shells is discouraged since accidentally changing to a restricted shell would prevent the user from ever changing her login shell
       back to its original value.

FILES

       /etc/passwd
           User account information.

       /etc/shells
           List of valid login shells.

       /etc/login.defs
           Shadow password suite configuration.

SEE ALSO

       chfn(1), login.defs(5), passwd(5).

shadow-utils 4.5                                                    01/25/2018                                                             CHSH(1)
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