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Full Discussion: Parsing null or empty output
Top Forums UNIX for Beginners Questions & Answers Parsing null or empty output Post 303009253 by MadeInGermany on Monday 11th of December 2017 12:58:18 PM
Old 12-11-2017
Quote:
Originally Posted by apmcd47
Code:
if [[ ${lastseen:-a} =~ [^0-9] ]]
then 
   echo "Serial number invalid"
   exit 3
fi

If lastseen is null or unset replace with an invalid string sequence. In this case the letter a will suffice.

Andrew
I call this a trick.
Nice somehow, but I am not going to recommend that as a common practice...
 

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nohup(1)						      General Commands Manual							  nohup(1)

NAME
nohup - run a command immune to hangups SYNOPSIS
command [arguments] DESCRIPTION
executes command with hangups and quits ignored. If output is not redirected by the user, both standard output and standard error are sent to If is not writable in the current directory, output is redirected to otherwise, fails. If a file is created, the file's permission bits will be set to If output from is redirected to a terminal, or is not redirected at all, the output is sent to EXTERNAL INFLUENCES
Environment Variables determines the language in which messages are displayed. If is not specified in the environment or is set to the empty string, the value of is used as a default for each unspecified or empty vari- able. If is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are set to "C". See environ(5). International Code Set Support Single- and multi-byte character code sets are supported. EXAMPLES
It is frequently desirable to apply to pipelines or lists of commands. This can be done only by placing pipelines and command lists in a single file, called a shell script. To run the script using features apply to the entire contents of file. If the shell script file is to be executed often, the need to type can be eliminated by setting execute permission on file. The script can also be run in the background with interrupts ignored (see sh(1)): file typically contains normal keyboard command sequences that one would want to continue running in case the terminal disconnects, such as: WARNINGS
Be careful to place punctuation properly. For example, in the command form: applies only to command1. To correct the problem, use the command form: Be careful of where standard error is redirected. The following command may put error messages on tape, making it unreadable: whereas puts the error messages into file EXIT STATUS
The following exit values are returned: The command specified by command was found but could not be invoked An error occurred in the nohup utility or the specified command could not be found Otherwise, the exit status of nohup will be that of the command specified. SEE ALSO
chmod(1), nice(1), sh(1), signal(5). STANDARDS CONFORMANCE
nohup(1)
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