Using pipes within variables Post: 302439000

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Top Forums Shell Programming and Scripting Using pipes within variables Post 302439000 by stv_t on Wednesday 21st of July 2010 10:33:17 AM

07-21-2010

Registered User

Using pipes within variables

Hi,

I'm trying avoid having a large number of 'if' statements in my script by setting up a variable within 'ksh' which can be expanded depending on parameters passed to the script. The output from the 'cat' command should be able pipe its output into any additional commands on the command line depending on the contents of the variable.

ie The code below should be able to list the complete file, only the executable lines, only the comment lines or be able to count the number of each type of line if required

Code:

extra_cmd=""

set -- $( getopt :ecl "$*" ) 

while [[ $1 != "--" ]] ; do
    case arg in
        "-e")  # Remove comments
                extra_cmd=" | grep -v \"^#\" " 
                ;;

        "-c") # Remove non comment lines
                extra_cmd=" | grep \"^#\" "
                ;;

         "-l")  # count lines
                extra_cmd="${extra_cmd} | wc -l "
                ;;

           *)  # Default
                extra_cmd=""           
                ;;
    esac
done
...
...
cat file ${extra_cmd}

However when this runs it displays the file on the screen rather than piping the output to 'grep' or 'wc' depending of the parameter passed to the script and then compains about the contents of the variable, which it takes as the name of another file to list

Quote:

cat: | grep -v "^#" : No such file or directory

I have tried a variety of different ways of quoting the contents or escaping the '|' when setting up the variable but none are having the desired effect of piping the output from 'cat' into 'grep' or 'wc'.

Any help would be greatly appreciated

Stv T

stv_t

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I already manage to get the output that i want.. but wat if removing all the pipes and convert it 1 liner with less pipes. My command below can get the ouput that i want. i just want to remove the pipes or less pipes. #cat file1 us-west-2a running i-3397a421...

LEARN ABOUT DEBIAN

shift

shift(1)							   User Commands							  shift(1)

NAME

       shift - shell built-in function to traverse either a shell's argument list or a list of field-separated words

SYNOPSIS

   sh
       shift [n]

   csh
       shift [variable]

   ksh
       * shift [n]

DESCRIPTION

   sh
       The positional parameters from $n+1 ... are renamed $1 ... . If n is not given, it is assumed to be 1.

   csh
       The  components of argv, or variable, if supplied, are shifted to the left, discarding the first component. It is an error for the variable
       not to be set or to have a null value.

   ksh
       The positional parameters from $n+1 $n+1 ... are renamed $1 ..., default n is 1. The parameter n can  be  any  arithmetic  expression  that
       evaluates to a non-negative number less than or equal to $#.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words,  following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
	   able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation  are  not
	   performed.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), ksh(1), sh(1), attributes(5)

SunOS 5.10							    15 Apr 1994 							  shift(1)

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