Copy content of multiple sh's into one Post: 302805603

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Top Forums Shell Programming and Scripting Copy content of multiple sh's into one Post 302805603 by Don Cragun on Friday 10th of May 2013 12:26:16 PM

05-10-2013

Registered User

Quote:

Originally Posted by verdepollo

KSH and Bash expansions are guaranteed to create an alphabetically sorted list of names before "feeding" it to cat.

Besides, file name expansion is performed before any redirection occurs.

Not sure about other shells.

Hi verdepollo,
You're correct. A POSIX conforming shell will perform pathname expansions before performing redirections.

Nonetheless, I have seen enough scripts fail because an output file was matched by an input pathname pattern expansion that I advise script writers to avoid the issue. When testing a new script and when a script fails for some reason and needs to be restarted, users frequently forget that they need to remove the output file before restarting the script. Even when it works, a user may want to run the script again the next day, week, or month and the output file can then accidentally become both an input file and an output file, leading to unexpected results. And if it is running on a system being shared with other users, the mistake can affect everyone using that filesystem; not just the user that forgot to remove the output file before restarting the script. Furthermore, when the script completes successfully, users often want to remove the (no longer needed) input files. If the output file matches the pattern that was used to select the input files, it is too easy to accidentally remove not only the input files, but also the output file.

Therefore, I strongly urge programmers not to create an output pathname that will be matched by the expansion of an input file pattern even though the output file should not be present when the script starts.

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shcomp

shcomp(1)							   User Commands							 shcomp(1)

NAME

       shcomp - compile a ksh93 shell script

SYNOPSIS

       shcomp [-nv] [infile [outfile]]

       shcomp -D [infile [outfile]]

DESCRIPTION

       If  the	-D  option  is not specified, shcomp takes a shell script, infile, and creates a binary format file, outfile, that ksh93 reads and
       executes with the same effect as the original script.

       Aliases are processed as the script is read. Alias definitions whose value requires variable expansion will not work correctly.

OPTIONS

       The following options are supported:

       -D	       Generate a list of strings that need to be placed in a message catalog for internationalization.
       --dictionary
		       With this option, all double quoted strings that are preceded by $ are printed, one literal  per  line.	A  literal  $"foo"
		       prints  "foo" in the output. These are the messages that need to be translated to locale specific versions for internation-
		       alization.

       -n	       Display warning messages for obsolete or non-conforming constructs.
       --noexec

       -v	       Display input from infile onto standard error as it reads it.
       --verbose

OPERANDS

       The following operands are supported:

       infile	  Specifies the name of the file that contains the shell script to be used as input.

		  If infile is omitted, the shell script is read from standard input.

       outfile	  Specifies the name of the output file.

		  If outfile is omitted, both modes write their results to standard output.

EXIT STATUS

       The following exit values are returned:

       0     Successful completion.

       >0    An error occurred.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |See below.		   |
       +-----------------------------+-----------------------------+

       The command-line interface and the system variables are Committed. The compiled shell code format is Private. The output of the	-D  option
       is Volatile.

SEE ALSO

       ksh93(1), attributes(5)

SunOS 5.11							    27 Jan 2009 							 shcomp(1)