例項)
現在我們來討論編寫一個指令碼的一般步驟。任何優秀的指令碼都應該具有幫助和輸入引數。並且寫一個偽指令碼（framework.sh），該指令碼包含了大多數指令碼都需要的框架結構，是一個非常不錯的主意。這時候，在寫一個新的指令碼時我們只需要執行一下copy命令：
cp framework.sh myscript
然後再插入自己的函式。
讓我們再看兩個例子：
二進位制到十進位制的轉換
指令碼b2d 將二進位制數 (比如 1101) 轉換為相應的十進位制數。這也是一個用expr命令進行數學運算的例子：
| 1 | #!/bin/sh |
| 2 | # vim: set sw=4 ts=4 et: |
| 3 | help() |
| 4 | { |
| 5 | cat < |
| 6 | b2h -- convert binary to decimal |
| 7 | USAGE: b2h [-h] binarynum |
| 8 | OPTIONS: -h help text |
| 9 | EXAMPLE: b2h 111010 |
| 10 | will return 58 |
| 11 | HELP |
| 12 | exit 0 |
| 13 | } |
| 14 | error() |
| 15 | { |
| 16 | # print an error and exit |
| 17 | echo "$1" |
| 18 | exit 1 |
| 19 | } |
| 20 | lastchar() |
| 21 | { |
| 22 | # return the last character of a string in $rval |
| 23 | if [ -z "$1" ]; then |
| 24 | # empty string |
| 25 | rval="" |
| 26 | return |
| 27 | fi |
| 28 | # wc puts some space behind the output this is why we need sed: |
| 29 | numofchar=`echo -n "$1" | wc -c | sed 's/ //g' ` |
| 30 | # now cut out the last char |
| 31 | rval=`echo -n "$1" | cut -b $numofchar` |
| 32 | } |
| 33 | |
| 34 | chop() |
| 35 | { |
| 36 | # remove the last character in string and return it in $rval |
| 37 | if [ -z "$1" ]; then |
| 38 | # empty string |
| 39 | rval="" |
| 40 | return |
| 41 | fi |
| 42 | # wc puts some space behind the output this is why we need sed: |
| 43 | numofchar=`echo -n "$1" | wc -c | sed 's/ //g' ` |
| 44 | if [ "$numofchar" = "1" ]; then |
| 45 | # only one char in string |
| 46 | rval="" |
| 47 | return |
| 48 | fi |
| 49 | numofcharminus1=`expr $numofchar "-" 1` |
| 50 | # now cut all but the last char: |
| 51 | rval=`echo -n "$1" | cut -b 0-${numofcharminus1}` |
| 52 | } |
| 53 | while [ -n "$1" ]; do |
| 54 | case $1 in |
| 55 | -h) help;shift 1;; # function help is called |
| 56 | --) shift;break;; # end of options |
| 57 | -*) error "error: no such option $1. -h for help";; |
| 58 | *) break;; |
| 59 | esac |
| 60 | done |
| 61 | # The main program |
| 62 | sum=0 |
| 63 | weight=1 |
| 64 | # one arg must be given: |
| 65 | [ -z "$1" ] && help |
| 66 | binnum="$1" |
| 67 | binnumorig="$1" |
| 68 | |
| 69 | while [ -n "$binnum" ]; do |
| 70 | lastchar "$binnum" |
| 71 | if [ "$rval" = "1" ]; then |
| 72 | sum=`expr "$weight" "+" "$sum"` |
| 73 | fi |
| 74 | # remove the last position in $binnum |
| 75 | chop "$binnum" |
| 76 | binnum="$rval" |
| 77 | weight=`expr "$weight" "*" 2` |
| 78 | done |
| 79 | echo "binary $binnumorig is decimal $sum" |
| 80 |
該指令碼使用的演算法是利用十進位制和二進位制數權值 (1,2,4,8,16,..)，比如二進位制"10"可以這樣轉換成十進位制：
0 * 1 + 1 * 2 = 2
為了得到單個的二進位制數我們是用了lastchar 函式。該函式使用wc –c計算字元個數，然後使用cut命令取出末尾一個字元。Chop函式的功能則是移除最後一個字元。