LinuxQuestions.org - need annotated explanation of the script !!

Hi i am new to linux and don't know about shell scripts. I need the detailed description of what each line of this shell script does.

1 #!/bin/bash
2 # makewhatis: create the whatis database
3
4 program=`basename $0`
5
6 # In case both /usr/man and /usr/share/man exist, the former is local
7 # and should be first.
8 # It is a bug to add /var/cache/man to DEFCATPATH.
9 dm=
10 for d in /usr/man /usr/share/man /usr/X11R6/man /usr/local/man
11 do
12 if [ -d $d ]; then
13 if [ x$dm = x ]; then dm=$d; else dm=$dm:$d; fi
14 fi
15 done
16 DEFMANPATH=$dm
17 dc=
18 for d in /usr/man/preformat /usr/man /usr/share/man/preformat /usr/share/man
19 do
20 if [ -d $d ]; then
21 if [ x$dc = x ]; then dc=$d; else dc=$dc:$d; fi
22 fi
23 done
24 DEFCATPATH=$dc
25
26 # make a single big /var/cache/man/whatis file,
27 DEFWHATISDIR=/var/cache/man
28 DEFWHATIS=$DEFWHATISDIR/whatis
29
30 AWK=/bin/awk
31
32 # Find a place for our temporary files.
33
34 if TMPFILE=$(mktemp /tmp/whatis.XXXXXX)
35 then
36
37 # make sure TMPFILE is deleted if program is killed or terminates
38 # (just delete this line if your shell doesnt know about trap)
39 trap "rm -rf $TMPFILE" 0
40 trap "rm -rf $TMPFILE; exit 255" 1 2 3 15
41
42 # default find arg: no directories, no empty files
43 findarg0="-type f -size +0"
44
45 topath=manpath
46
47 defmanpath=$DEFMANPATH
48 defcatpath=
49
50 if [ -n "$MANSECT" ]; then
51 sections=$MANSECT
52 else
53 sections=`$AWK '($1 == "MANSECT") { print $2 }' /etc/man.config`
54 if [ x"$sections" = x ]; then
55 sections="1:1p:8:2:3:3p:4:5:6:7:9:0p:tcl:n:l"
56 fi
57 fi
58 sections=`echo $sections | sed -e 's/:/ /g'`
59
60 whatisdb=$DEFWHATIS
61
62 for name in "$@"
63 do
64 if [ -n "$setsections" ]; then
65 setsections=
66 sections=$name
67 continue
68 fi
69 if [ -n "$setwhatis" ]; then
70 setwhatis=
71 whatisdb=$name
72 continue
73 fi
74 case $name in
75 --version|-V)
76 echo "$program from man-1.6f"
77 exit 0;;
78 -c) topath=catpath
79 defmanpath=
80 defcatpath=$DEFCATPATH
81 continue;;
82 -s) setsections=1
83 continue;;
84 -o) setwhatis=1
85 continue;;
86 -U) [ -f "$whatisdb" ] && findarg="-cnewer $whatisdb"
87 update=1
88 continue;;
89 -u) findarg="-ctime 0"
90 update=1
91 continue;;
92 -v) verbose=1
93 continue;;
94 -w) manpath=`man --path`
95 catpath=$manpath
96 continue;;
97 -*) echo "Usage: makewhatis [-s sections] [-u] [-v] [-w] [manpath] [-c [catpath]] [-o whatisdb]"
98 echo " This will build the whatis database for the man pages"
99 echo " found in manpath and the cat pages found in catpath."
100 echo " -s: sections (default: $sections)"
101 echo " -u: update database with pages added today"
102 echo " -U: update database with pages added since last makewhatis run"
103 echo " -v: verbose"
104 echo " -o: location of whatis database (default: $DEFWHATIS)"
105 echo " -w: use manpath obtained from \`man --path\`"
106 echo " [manpath]: man directories (default: $DEFMANPATH)"
107 echo " [catpath]: cat directories (default: the first existing"
108 echo " directory in $DEFCATPATH)"
109 exit;;
110 *) if [ -d $name ]
111 then
112 eval $topath="\$$topath":$name
113 else
114 echo "No such directory $name"
115 exit
116 fi;;
117 esac
118 done
119
120 manpath=`echo ${manpath-$defmanpath} | tr : ' '`
121 if [ x"$catpath" = x ]; then
122 for d in `echo $defcatpath | tr : ' '`
123 do
124 if [ -d $d ]; then catpath=$d; break; fi
125 done
126 fi
127 catpath=`echo ${catpath} | tr : ' '`