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Full Discussion: Odd(?) shell script practise
The Lounge What is on Your Mind? Odd(?) shell script practise Post 302803899 by MadeInGermany on Tuesday 7th of May 2013 04:08:19 PM
Old 05-07-2013
Odd(?) shell script practise
Hello,
I often stumble over a common shell coding practise.
Example 1:
Code:
#!/bin/sh 
# 
# Licensed Materials - Property of IBM
# Rational ClearCase
# (C) Copyright IBM Corp. 1999, 2010.  All Rights Reserved
# US Government Users Restricted Rights -
# Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp
# 
# Start/Stop ClearCase daemons as well as
# mount or umount MVFS file systems.
#
...
INSMOD="/sbin/insmod -f"
MODPROBE="/sbin/modprobe"
RMMOD=/sbin/rmmod
LSMOD=/sbin/lsmod
PIDOF=/sbin/pidof
ECHO="/bin/echo -e "
NAWK=/bin/awk
GREP=/bin/grep
RM=/bin/rm
PS=/bin/ps
CP=/bin/cp
LN=/bin/ln
MKDIR=/bin/mkdir
EXPR=/usr/bin/expr
...

Example 2:
Code:
#!/bin/ksh
# OPC_WHAT_STRING="@(#)HP Operations Smart Plug-in for Databases 11.40.000 (10/22/08)"

########################################################################
#
# File:         spi_migrate.sh
# Description:  determines the DCE / HTTPS agent environment and starts
#               migration of all available SPIs
# Language:     Bourne Shell
# Package:      -none-
#
# (c) Copyright 2004 Hewlett-Packard Development Company, L.P. 
#
########################################################################
# set -x

ECHO=echo
CAT=cat
MYSYS=`uname -s`
if [ $MYSYS = "HP-UX" ] ; then
  GREP=/usr/bin/grep
  AWK=/usr/bin/awk
  SED=/usr/bin/sed
  DIFF=/usr/bin/diff
elif [ $MYSYS = "SunOS" ] ; then
  GREP=/usr/xpg4/bin/grep
  AWK=/usr/xpg4/bin/awk
  SED=/usr/xpg4/bin/sed
  DIFF=diff
elif [ $MYSYS = "AIX" ] ; then
  GREP=/usr/bin/grep
  AWK=/usr/bin/awk
  SED=/usr/bin/sed
  DIFF=/usr/bin/diff
elif [ $MYSYS = "OSF" ] ; then
  GREP=/usr/bin/grep
  AWK=/usr/bin/awk
  SED=/usr/bin/sed
  DIFF=/usr/bin/diff
elif [ $MYSYS = "Linux" ] ; then
  GREP=grep
  AWK=awk
  DIFF=diff
  ECHO='echo -e'
...

Example3:
Code:
#! /bin/sh
#
# Log file pattern detector plugin for Nagios
# Written by Ethan Galstad (nagios@nagios.org)
# Last Modified: 07-31-1999
#
...
# Paths to commands used in this script.  These
# may have to be modified to match your system setup.
# TV: removed PATH restriction. Need to think more about what this means overall
#PATH=""

ECHO="/bin/echo"
GREP="/bin/egrep"
DIFF="/usr/bin/diff"
TAIL="/usr/bin/tail"
CAT="/bin/cat"
RM="/bin/rm"
CHMOD="/bin/chmod"
TOUCH="/bin/touch"

Do you see what is in common?
Always define all commands with its platform-dependent path and store it in UPPERCASE variables.
Sometimes I even see a for loop that finds out where a command lives and stores the result - in an UPPERCASE variable.
Always UPPERCASE!

And later in the scripts there is of course
Code:
$ECHO ... | $GREP ... | $AWK ... | $WC ...

instead of
Code:
echo ... | grep ... | awk ... | wc ...

My Questions:

1. have you met that, too?
2. Is there a book or a University that teaches this?
 

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