Difficulty with CAT redirection in script Post: 302990335

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Top Forums Shell Programming and Scripting Difficulty with CAT redirection in script Post 302990335 by bakunin on Wednesday 25th of January 2017 04:05:15 AM

01-25-2017

Registered User

Quote:

Originally Posted by demmith

Oh my God, I am such an idiot! LOL!

Don't worry, it happens to the best of us.

As a general rule: do not change directories inside a script at all (for exactly this reason, to avoid this confusion). Whenever you work on files make sure you always use absolute pathes like this:

Code:

# cat wrong.sh

cd /some/where
command > ./output.file

# cat correct.sh

outdir="/some/where"
command > "${outdir}/output.file"

The same goes for all other filenames. This way your script will work regardless of where you started it. If you work on several files using a variable for the directory part ensures they all land in the same place. The absolute worst you can do, though, is to use relative pathes:

Code:

# cat worst-of-worst.sh

command1 > outfile1
cd ..
command2 > outfile2

If you ever find that in anyones code: have them promise never to write any shell script again. This is a surefire recipe for disaster because the script will (maybe) work if you call it from one directory and fail if you call it from another.

In general the script you call inherits the environment from its calling process - the command shell you used to call it. "Envrionent" means not only the values for variables (all that have been "export"ed before) like PATH, TZ (timezone), LANG, etc.. but also the current directory and similar things. It is good practice to make your script independent from this environment by setting it to a certain state except for the few variables where you explicitly want this effect to take place. This includes (but is not limited to) making it independent of the current path it was called from.

I hope this helps.

bakunin

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LEARN ABOUT HPUX

nohup

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)