Shell编程基础

• 1 从第一行开始
• 2 变量
  • 2.1 变量赋值和引用
  • 2.2 变量算术
• 3 Shell里的流程控制
  • 3.1 if 语句
  • 3.2 && 和 || 操作符
  • 3.3 case 语句
  • 3.4 select 循环语句
  • 3.5 while/for 循环
• 4 Shell里的一些特殊符号
  • 4.1 引号
• 5 Here Document
• 6 Shell里的函数
• 7 命令行参数
• 8 Shell脚本示例
  • 8.1 一般编程步骤
  • 8.2 二进制到十进制的转换
  • 8.3 文件循环移动
• 9 脚本调试

#!/bin/bash

chmod +x filename

varname=值 [var2=val2 ....]

# assign
a="hello world"  # 等号两边均不能有空格存在
# print
printf ‘%s\n‘ "A is: $a"

A is: hello world

num=2
echo "this is the $numnd"   # 输出 this is the       — shell 尝试寻找 $numnd 的值
echo "this is the ${num}nd" # 输出 this is the 2nd   — 修好了！
# 花括号可以隔开变量名，但是放歪了的话…
echo "this is the {$num}nd" # 输出 this is the {2}nd — 切是切开了，但是…

var=1
var=$var+1
echo $var # 输出 1+1

var=0
# bash 里面可以用 (( )) 执行 C 风格的算术表达式。
# 如果你接下来还会读 if 那一段的话，你还会知道这玩意的返回和 C 的非零真假判断一致。
(( var += 1 )) # 这是一种，现在 var 是 1
(( var++ ))    # 这也是一种自增，2
(( var = var * var )) # 怎么来乘法了！var 现在是 4。
let ‘var = var / 3‘   # 还是只有 bash 才能用的拓展。除法是整数除法，向 0 舍入，1。
# 来一点不一定要 bash 的方法吧，毕竟 sh 还有很多种，总不能全报错了吧。
# $(( )) 会展开成为这个 C 表达式求值的结果。以前 bash 有个 $[ ] 一样，但是别去用。
echo $((var += 2))    # echo 出 3，var 现在是 3。
var=$((var-1))        # 展开成 var=2，var 现在是……还用说吗，2。

var=1
var=$(expr "$var" + 1) # expr 收到三个参数 ‘1‘ ‘+‘ ‘1‘，

                      # 按照 expr --help 里面写的方法运行
                      # 然后输出替换掉 $() 这里变成 var=2。

var=`expr "$var" + 1`  # 前面一行的老写法，千万千万不要学。

if 
  判断命令，可以有很多个，真假取最后的返回值
then
  如果前述为真做什么
[ # 方括号代表可选，别真打进去了！
elif
  可以再来个判断，如果签名为假继续尝试这里
then
  如果前述为真做什么 ]
else
  如果全都不行做什么
fi # 结束，就是倒写的 if 啦。

if ....; then # 你也可以写成 if 之后换行，这样就不用分号了。
  ....
fi

if [ "${SHELL}" == "/bin/bash" ]; then
  echo "your login shell is the bash (bourne again shell)"
else
  echo "your login shell is not bash but ${SHELL}"
fi

[ -f "/etc/shadow" ] && echo "This computer uses shadow passwords"

#!/bin/bash

mailfolder=/var/spool/mail/james
[ -r "$mailfolder" ] || { echo "Can not read $mailfolder"; exit 1; }
echo "$mailfolder has mail from:"
grep "^From " $mailfolder

{
  echo "Can not read $mailfolder"; # 打印错误信息
  exit 1; # 退出程序
}

case ... in
   ...) do something here 
   ;;
esac

lf.gz: gzip compressed data, deflated, original filename,
last modified: Mon Aug 27 23:09:18 2001, os: Unix

#!/bin/bash

ftype="$(file "$1")"
case "$ftype" in
"$1: Zip archive"*)
   unzip "$1" ;;
"$1: gzip compressed"*)
   gunzip "$1" ;;
"$1: bzip2 compressed"*)
   bunzip2 "$1" ;;
*)
   echo "File $1 can not be uncompressed with smartzip";;
esac

smartzip articles.zip

pocket=()
select var in 跳跳糖 糖 很多糖 企鹅糖; do
  echo "除了 $var 还要什么吗？"
  if ((RANDOM%4 == 0)); then
    echo "呀！时间不够了，快上车！"
    break # break 还是那个 break
  fi
  pocket+=("$var")
done
echo "你最后说的那个 $var 弄丢了……"
IFS=‘、‘
echo "现在口袋里只有：${pocket[*]}。"
IFS=$‘ \t\n‘

#!/bin/bash

echo "What is your favourite OS?"
select var in "Linux" "Gnu Hurd" "Free BSD" "Other"; do
  break;
done
echo "You have selected $var"

What is your favourite OS?
1) Linux
2) Gnu Hurd
3) Free BSD
4) Other
#? 1
You have selected Linux

while ...; do
   ....
done

for var in ....; do
   ....
done

#!/bin/bash

for var in A B C ; do
   echo "var is $var"
done

#!/bin/bash

# list a content summary of a number of RPM packages
# USAGE: showrpm rpmfile1 rpmfile2 ...
# EXAMPLE: showrpm /cdrom/RedHat/RPMS/*.rpm
for rpmpackage in "$@"; do
   if [ -r "$rpmpackage" ];then
      echo "=============== $rpmpackage =============="
      rpm -qi -p $rpmpackage
   else
      echo "ERROR: cannot read file $rpmpackage"
   fi
done

#!/bin/bash

echo *.jpg   # => mail.jpg tux.jpg

#!/bin/bash

echo "*.jpg"  # => *.jpg
echo ‘*.jpg‘  # => *.jpg

#!/bin/bash

echo $SHELL   # => /bin/bash
echo "$SHELL" # => /bin/bash
echo ‘$SHELL‘ # => $SHELL

echo \*.jpg   # => *.jpg
echo \$SHELL  # => $SHELL

#!/bin/bash

# we have less than 3 arguments. Print the help text:
if [ $# -lt 3 ] ;; then
cat << HELP

ren -- renames a number of files using sed regular expressions USAGE: ren ‘regexp‘ ‘replacement‘ files...

EXAMPLE: rename all *.HTM files in *.html:
   ren ‘HTM$‘ ‘html‘ *.HTM

HELP                #这里HELP要顶格写，前面不能有空格或者TAB制表符。如果cat一行写成cat &lt;&lt; -HELP，前边可以带TAB.
   exit 0
fi
OLD="$1"
NEW="$2"
# The shift command removes one argument from the list of
# command line arguments.
shift
shift
# $@ contains now all the files:
for file in "$@"; do
   if [ -f "$file" ]&nbsp;; then
      newfile=`echo "$file" | sed "s/${OLD}/${NEW}/g"`
      if [ -f "$newfile" ]; then
　　　　   echo "ERROR: $newfile exists already"
      else
         echo "renaming $file to $newfile ..."
         mv "$file" "$newfile"
      fi
   fi
done

# 别笑，bash 里面函数名的确可以这样……
# (POSIX sh 函数名倒是和变量名要求差不多)
我是一个函数() {
  # 函数里面 $1 $2 对应函数所接受到的第一、第二……个参数。
  这里有很多命令
}

#!/bin/bash

help()
{
cat << HELP
xtitlebar -- change the name of an xterm, gnome-terminal or kde konsole
USAGE: xtitlebar [-h] "string_for_titelbar"
OPTIONS: -h help text
EXAMPLE: xtitlebar "cvs"
HELP
exit 0
}
# in case of error or if -h is given we call the function help:
if [[ $1 == ‘‘ || $1 == ‘-h‘ ]]; then
  help
fi
# send the escape sequence to change the xterm titelbar:
echo -e "\033]0;$1\007"
#

#!/bin/bash
 
help()
{
   cat << HELP
   This is a generic command line parser demo.
   USAGE EXAMPLE: cmdparser -l hello -f -- -somefile1 somefile2
HELP
   exit 0
}
  
while [ -n "$1" ]; do
case "$1" in
   -h) help;shift 1;; # function help is called
   -f) opt_f=1;shift 1;; # variable opt_f is set
   -l) opt_l=$2;shift 2;; # -l takes an argument -> shift by 2
   --) shift;break;; # end of options
   -*) echo "error: no such option $1. -h for help";exit 1;;
   *) break;;
esac
done
 
echo "opt_f is $opt_f"
echo "opt_l is $opt_l"
echo "first arg is $1"
echo "2nd arg is $2"

cmdparser -l hello -f -- -somefile1 somefile2

opt_f is 1
opt_l is hello
first arg is -somefile1
2nd arg is somefile2

cp framework.sh myscript

#!/bin/bash
# vim: set sw=4 ts=4 et:
help()
{
   cat << HELP
   
b2d -- convert binary to decimal
 
USAGE: b2d [-h] binarynum
 
OPTIONS: -h help text
 
EXAMPLE: b2d 111010
will return 58
HELP
   exit 0
}
 
error()
{
   # print an error and exit
   echo "$1"
   exit 1
}
 
lastchar()
{
   # return the last character of a string in $rval
   if [ -z "$1" ]; then
      # empty string
      rval=""
      return
   fi
   # wc puts some space behind the output this is why we need sed:
   numofchar=`echo -n "$1" | sed ‘s/ //g‘ | wc -c ` 
   #sed ‘s/ //g‘  所有空白去掉  sed ‘s/ /\t/g‘ 所有空白用t代替
   # now cut out the last char  抓取第numofchar个字节
   rval=`echo -n "$1" | cut -b $numofchar`
}
 
chop()
{
   # remove the last character in string and return it in $rval
   if [ -z "$1" ]; then
      # empty string
      rval=""
      return
   fi
   # wc puts some space behind the output this is why we need sed:
   numofchar=`echo -n "$1" | wc -c | sed ‘s/ //g‘ `
   if [ "$numofchar" = "1" ]; then
      # only one char in string
      rval=""
      return
   fi
   numofcharminus1=`expr $numofchar "-" 1`
   # now cut all but the last char:
   rval=`echo -n "$1" | cut -b -$numofcharminus1` 
   #原来的 rval=`echo -n "$1" | cut -b 0-${numofcharminus1}`运行时出错.
   #原因是cut从1开始计数，应该是cut -b 1-${numofcharminus1}
}
 
while [ -n "$1" ]; do
case $1 in
   -h) help;shift 1;; # function help is called
   --) shift;break;; # end of options
   -*) error "error: no such option $1. -h for help";;
   *) break;;
esac
done

# The main program
sum=0
weight=1
# one arg must be given:
[ -z "$1" ] &amp;&amp; help
binnum="$1"
binnumorig="$1"
 
while [ -n "$binnum" ]; do
   lastchar "$binnum"
   if [ "$rval" = "1" ]; then
      sum=`expr "$weight" "+" "$sum"` 
      # $expr 10 + 10    20 expr提示是计算操作
   fi
   # remove the last position in $binnum
   chop "$binnum"
   binnum="$rval"
   weight=`expr "$weight" "*" 2`
done
 
echo "binary $binnumorig is decimal $sum"
#

0 * 1 + 1 * 2 = 2

#!/bin/bash
while read -p ‘input a binary...‘ num; do
  if [[ $num == *[!01]* ]]; then
    echo "含有 0 1 之外的字符"
  fi
  echo "$((0x$num))"      # 在 num 头上糊一个 0x 然后跑数学计算——就完事了！
  printf "%d\n" "0x$num"    # printf 也可以凑热闹啊
done

#!/bin/bash
# 人人皆知的 Horner 规则
value=0
echo "写一堆 1 0 完了回车"
while read -n 1 char; do
  case $char in
    (0|1) ;;      # 好
    (‘‘)  break;; # 没了
    (*)   echo "你说啥？"; break;;
  esac
  ((value *= 2))
  ((value += char))
done
echo "$value"

#!/bin/bash
# vim: set sw=4 ts=4 et:
 
ver="0.1"
help()
{
   cat << HELP
   rotatefile -- rotate the file name
   USAGE: rotatefile [-h] filename
   OPTIONS: -h help text
   EXAMPLE: rotatefile out
 
   This will e.g rename out.2 to out.3, out.1 to out.2, out to out.1
   and create an empty out-file
 

   version $ver

HELP

   exit 0
}

if [[ $1 == ‘-h‘ || $1 == ‘‘ ]]; then
  help
fi

filename=$1

# 我们先找到最大的数字再说。
max=0
while [ -f "$filename.$((++max))" ]; do
  : # 什么都不用做，我们已经顺手用 ++max 自增了 max 了。
done

# 然后从最大的一路重命名下来。
for ((i=max; i>0; i--)); do
  # 数字加个 1，好给前一个让位子。
  mv "$filename.$i" "$filename.$((i+1))"
done
 
# 最后我们点名要重命名的：
if [ -f "$filename" ]; then
   mv "$filename" "$filename.1"
fi

# 重新创建一下。
: > "$filename"

sh -x strangescript

sh -n your_script

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