Back ticks and $() Post: 302843194

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Top Forums Shell Programming and Scripting Back ticks and $() Post 302843194 by bobbygsk on Monday 12th of August 2013 10:27:50 AM

08-12-2013

Registered User

Back ticks and $()

In one of my previous threads, someone suggested not to use backticks. When I googled, I came to know that back ticks are deprecated instead $() should be used. But I face issue while using $().
Note: I used echo of the sql just to debug.

The following is the code

Code:

#!/bin/ksh
#set -x
ScriptDir=$(dirname $0)
. ${ScriptDir}/setEnv.sh
VAL=X

  echo "\$(sqlplus -s $user_name/$user_pwd@$database_name <<EOF
     set pagesize 0 LINESIZE 1000 feedback off verify off heading off echo off
     select count(1) from dual where dummy = '$VAL';
    EXIT;
  EOF)"

  REC_EXIST=$(sqlplus -s $user_name/$user_pwd@$database_name <<EOF
  set pagesize 0 LINESIZE 1000 feedback off verify off heading off echo off
  select count(1) from dual where dummy = '$VAL';
  EXIT;
  EOF)

  echo "CHECK RUN STATUS"
  run_status=$?
  echo "RUN STATUS    : $run_status"
  echo "REC_EXIST      : $REC_EXIST"

  if [ $REC_EXIST == 0 ] ;then
    echo "No Records    : $REC_EXIST"
  else
    echo "Records exists: $REC_EXIST"
  fi

The above code works fine as long as I use back tick. When I replace backticks with $(), I encounter the following error

Code:

$(sqlplus -s xxxxxxx/xxxxx@xxxxxxx <<EOF
       set pagesize 0 LINESIZE 1000 feedback off verify off heading off echo off
       select count(1) from dual where dummy = 'X';
       EXIT;
       EOF)


CHECK RUN STATUS
RUN STATUS    : 0
REC_EXIST     :   select count(1) from dual where dummy = "$VAL"
                                          *
ERROR at line 1:
ORA-00904: "$VAL": invalid identifier
test.sh[XX]: count(1): unknown test operator
Records exists:   select count(1) from dual where dummy = "$VAL"
                                          *
ERROR at line 1:
ORA-00904: "$VAL": invalid identifier
Records exists:   select count(1) from dual where dummy = "$VAL"
                                          *
ERROR at line 1:
ORA-00904: "$VAL": invalid identifier

By using $() I got good results for other scripts. Can anyone explain what went wrong.
Appreciate your response

bobbygsk

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LEARN ABOUT SUNOS

echo

echo(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME

       echo - echo arguments to standard output

SYNOPSIS

       /usr/ucb/echo [-n] [argument]

DESCRIPTION

       echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output.

       echo  is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi-
       ronment variables.

       For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:

	 o  echo your current-working-directory's full pathname

	 o  pipe the output through tr to translate the path's embedded slash-characters into space-characters

	 o  pipe that output through wc -w for a count of the names in your path.

	      example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w"

       See tr(1) and wc(1) for their functionality.

       The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be  invoked	if
       the  user  calls  echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape
       characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the  black-slashed  escape  characters,	and  ksh's
       echo() also understands a as the audible bell character; however, these commands do not have an -n option.

OPTIONS

       -n	Do not add the NEWLINE to the output.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), echo(1), ksh(1), sh(1), tr(1),  wc(1), attributes(5)

NOTES

       The -n option is a transition aid for BSD applications, and may not be supported in future  releases.

SunOS 5.10							    3 Aug 1994								  echo(1B)