explaination of shell script required

shaz · Post by **shaz** » Tue Apr 13, 2004 4:10 am

i'm new to linux .so please explain this following shell script.

#! /bin/sh
# Guess values for system-dependent variables and create 
## --------------------- ##
## M4sh Initialization.  ##
## --------------------- ##

# Be Bourne compatible
if test -n "${ZSH_VERSION+set}" && (emulate sh) >/dev/null 2>&1; then
  emulate sh
  NULLCMD=:
  # Zsh 3.x and 4.x performs word splitting on ${1+"$@"}, which
  # is contrary to our usage.  Disable this feature.
  alias -g '${1+"$@"}'='"$@"'
elif test -n "${BASH_VERSION+set}" && (set -o posix) >/dev/null 2>&1; then
  set -o posix
fi
DUALCASE=1; export DUALCASE # for MKS sh

# Support unset when possible.
if ( (MAIL=60; unset MAIL) || exit) >/dev/null 2>&1; then
  as_unset=unset
else
  as_unset=false
fi


# Work around bugs in pre-3.0 UWIN ksh.
$as_unset ENV MAIL MAILPATH
PS1='$ '
PS2='> '
PS4='+ '

# NLS nuisances.
for as_var in \
  LANG LANGUAGE LC_ADDRESS LC_ALL LC_COLLATE LC_CTYPE LC_IDENTIFICATION \
  LC_MEASUREMENT LC_MESSAGES LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER \
  LC_TELEPHONE LC_TIME
do
  if (set +x; test -z "`(eval $as_var=C; export $as_var) 2>&1`"); then
    eval $as_var=C; export $as_var
  else
    $as_unset $as_var
  fi
done

# Required to use basename.
if expr a : '\(a\)' >/dev/null 2>&1; then
  as_expr=expr
else
  as_expr=false
fi

if (basename /) >/dev/null 2>&1 && test "X`basename / 2>&1`" = "X/"; then
  as_basename=basename
else
  as_basename=false
fi


# Name of the executable.
as_me=`$as_basename "$0" ||
$as_expr X/"$0" : '.*/\([^/][^/]*\)/*$' \| \
    X"$0" : 'X\(//\)$' \| \
    X"$0" : 'X\(/\)$' \| \
    .     : '\(.\)' 2>/dev/null ||
echo X/"$0" |
    sed '/^.*\/\([^/][^/]*\)\/*$/{ s//\1/; q; }
       /^X\/\(\/\/\)$/{ s//\1/; q; }
       /^X\/\(\/\).*/{ s//\1/; q; }
       s/.*/./; q'`