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		<a xmlns="" href="mailto:netkiller@msn.com">Email</a><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">1.3. variable</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="introduction.html">上一页</a> </td><th width="60%" align="center">第 1 章 Bash Shell</th><td width="20%" align="right"> <a accesskey="n" href="conditions.html">下一页</a></td></tr></table><hr /></div><table xmlns=""><tr><td><iframe src="http://ghbtns.com/github-btn.html?user=netkiller&amp;repo=netkiller.github.io&amp;type=watch&amp;count=true&amp;size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="http://ghbtns.com/github-btn.html?user=netkiller&amp;repo=netkiller.github.io&amp;type=fork&amp;count=true&amp;size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="http://ghbtns.com/github-btn.html?user=netkiller&amp;type=follow&amp;count=true&amp;size=large" height="30" width="240" frameborder="0" scrolling="0" style="width:240px; height: 30px;" allowTransparency="true"></iframe></td></tr></table><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="variable"></a>1.3. variable</h2></div></div></div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="expression"></a>1.3.1. 表达式</h3></div></div></div>
		<pre class="screen">
!!：再次执行上一条命令
!$：上一条命令的最后一个单词
{a..b}：按照从a到b顺序的一个数字列表
{a,b,c}：三个词a,b,c. 可以这样使用 touch /tmp/{a,b,c}
{$1-$9}：执行shell脚本时的命令行参数
$0：正在执行的命令名称
$#：当前启动的命令中传入的参数个数
$?：上一条命令的执行返回值。
$$：该shell的进程号。
$*：从$1开始，启动该shell脚本的所有参数。
		<pre class="screen">
$ mkdir -p {a..z}
a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z
$ mkdir -p {a..z}{0..9}
a0  b0  c0  d0  e0  f0  g0  h0  i0  j0  k0  l0  m0  n0  o0  p0  q0  r0  s0  t0  u0  v0  w0  x0  y0  z0
a1  b1  c1  d1  e1  f1  g1  h1  i1  j1  k1  l1  m1  n1  o1  p1  q1  r1  s1  t1  u1  v1  w1  x1  y1  z1
a2  b2  c2  d2  e2  f2  g2  h2  i2  j2  k2  l2  m2  n2  o2  p2  q2  r2  s2  t2  u2  v2  w2  x2  y2  z2
a3  b3  c3  d3  e3  f3  g3  h3  i3  j3  k3  l3  m3  n3  o3  p3  q3  r3  s3  t3  u3  v3  w3  x3  y3  z3
a4  b4  c4  d4  e4  f4  g4  h4  i4  j4  k4  l4  m4  n4  o4  p4  q4  r4  s4  t4  u4  v4  w4  x4  y4  z4
a5  b5  c5  d5  e5  f5  g5  h5  i5  j5  k5  l5  m5  n5  o5  p5  q5  r5  s5  t5  u5  v5  w5  x5  y5  z5
a6  b6  c6  d6  e6  f6  g6  h6  i6  j6  k6  l6  m6  n6  o6  p6  q6  r6  s6  t6  u6  v6  w6  x6  y6  z6
a7  b7  c7  d7  e7  f7  g7  h7  i7  j7  k7  l7  m7  n7  o7  p7  q7  r7  s7  t7  u7  v7  w7  x7  y7  z7
a8  b8  c8  d8  e8  f8  g8  h8  i8  j8  k8  l8  m8  n8  o8  p8  q8  r8  s8  t8  u8  v8  w8  x8  y8  z8
a9  b9  c9  d9  e9  f9  g9  h9  i9  j9  k9  l9  m9  n9  o9  p9  q9  r9  s9  t9  u9  v9  w9  x9  y9  z9
$ touch  {a..z}{0..9}/{a..z}{0..9}
a0  b0  c0  d0  e0  f0  g0  h0  i0  j0  k0  l0  m0  n0  o0  p0  q0  r0  s0  t0  u0  v0  w0  x0  y0  z0
a1  b1  c1  d1  e1  f1  g1  h1  i1  j1  k1  l1  m1  n1  o1  p1  q1  r1  s1  t1  u1  v1  w1  x1  y1  z1
a2  b2  c2  d2  e2  f2  g2  h2  i2  j2  k2  l2  m2  n2  o2  p2  q2  r2  s2  t2  u2  v2  w2  x2  y2  z2
a3  b3  c3  d3  e3  f3  g3  h3  i3  j3  k3  l3  m3  n3  o3  p3  q3  r3  s3  t3  u3  v3  w3  x3  y3  z3
a4  b4  c4  d4  e4  f4  g4  h4  i4  j4  k4  l4  m4  n4  o4  p4  q4  r4  s4  t4  u4  v4  w4  x4  y4  z4
a5  b5  c5  d5  e5  f5  g5  h5  i5  j5  k5  l5  m5  n5  o5  p5  q5  r5  s5  t5  u5  v5  w5  x5  y5  z5
a6  b6  c6  d6  e6  f6  g6  h6  i6  j6  k6  l6  m6  n6  o6  p6  q6  r6  s6  t6  u6  v6  w6  x6  y6  z6
a7  b7  c7  d7  e7  f7  g7  h7  i7  j7  k7  l7  m7  n7  o7  p7  q7  r7  s7  t7  u7  v7  w7  x7  y7  z7
a8  b8  c8  d8  e8  f8  g8  h8  i8  j8  k8  l8  m8  n8  o8  p8  q8  r8  s8  t8  u8  v8  w8  x8  y8  z8
a9  b9  c9  d9  e9  f9  g9  h9  i9  j9  k9  l9  m9  n9  o9  p9  q9  r9  s9  t9  u9  v9  w9  x9  y9  z9
a0  b0  c0  d0  e0  f0  g0  h0  i0  j0  k0  l0  m0  n0  o0  p0  q0  r0  s0  t0  u0  v0  w0  x0  y0  z0
a1  b1  c1  d1  e1  f1  g1  h1  i1  j1  k1  l1  m1  n1  o1  p1  q1  r1  s1  t1  u1  v1  w1  x1  y1  z1
a2  b2  c2  d2  e2  f2  g2  h2  i2  j2  k2  l2  m2  n2  o2  p2  q2  r2  s2  t2  u2  v2  w2  x2  y2  z2
a3  b3  c3  d3  e3  f3  g3  h3  i3  j3  k3  l3  m3  n3  o3  p3  q3  r3  s3  t3  u3  v3  w3  x3  y3  z3
a4  b4  c4  d4  e4  f4  g4  h4  i4  j4  k4  l4  m4  n4  o4  p4  q4  r4  s4  t4  u4  v4  w4  x4  y4  z4
a5  b5  c5  d5  e5  f5  g5  h5  i5  j5  k5  l5  m5  n5  o5  p5  q5  r5  s5  t5  u5  v5  w5  x5  y5  z5
a6  b6  c6  d6  e6  f6  g6  h6  i6  j6  k6  l6  m6  n6  o6  p6  q6  r6  s6  t6  u6  v6  w6  x6  y6  z6
a7  b7  c7  d7  e7  f7  g7  h7  i7  j7  k7  l7  m7  n7  o7  p7  q7  r7  s7  t7  u7  v7  w7  x7  y7  z7
a8  b8  c8  d8  e8  f8  g8  h8  i8  j8  k8  l8  m8  n8  o8  p8  q8  r8  s8  t8  u8  v8  w8  x8  y8  z8
a9  b9  c9  d9  e9  f9  g9  h9  i9  j9  k9  l9  m9  n9  o9  p9  q9  r9  s9  t9  u9  v9  w9  x9  y9  z9
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="environment"></a>1.3.2. Internal Environment Variables</h3></div></div></div>
		<a class="ulink" href="http://tldp.org/LDP/abs/html/internalvariables.html" target="_top">http://tldp.org/LDP/abs/html/internalvariables.html</a>
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.set"></a>1.3.3. set 设置变量</h3></div></div></div>
		<pre class="screen">
$ set -- `echo aa bb cc`
$ set -- aa bb cc
    <div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="unset"></a>1.3.4. unset 变量销毁</h3></div></div></div>
    		<pre class="screen">
$ unset logfile
    		</pre>
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.default"></a>1.3.5. 设置变量默认值</h3></div></div></div>
   		<p>如果 logfile 值已经存在侧不会覆盖</p>
   		<pre class="screen">
$ logfile=/var/log/test.log
$ echo $logfile
/var/log/test.log
$ logfile=${logfile:-/tmp/test.log}
$ echo $logfile
/var/log/test.log
    	</pre>
    	<p>如果变量为空才能设置</p>
    	<pre class="screen">
$ unset logfile
$ logfile=${logfile:-/tmp/test.log}
$ echo $logfile
/tmp/test.log
    	</pre>
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.export"></a>1.3.6. export 设置全局变量</h3></div></div></div>
		<pre class="screen">
export CATALINA_OUT=/www/logs/tomcat/catalina.out
		<p>unset 销毁变量</p>
		<pre class="screen">
unset CATALINA_OUT
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.declare"></a>1.3.7. declare</h3></div></div></div>
		<pre class="screen">
功能说明：声明 shell 变量。
语　　法：declare [+/-][rxi][变量名称＝设置值] 或 declare -f
补充说明：declare为shell指令，在第一种语法中可用来声明变量并设置变量的属性([rix]即为变量的属性），在第二种语法中可用来显示shell函数。若不加上任何参数，则会显示全部的shell变量与函数(与执行set指令的效果相同)。
　+/- 　"-"可用来指定变量的属性，"+"则是取消变量所设的属性。
　-f 　仅显示函数。
　r 　将变量设置为只读。
　x 　指定的变量会成为环境变量，可供shell以外的程序来使用。
　i 　[设置值]可以是数值，字符串或运算式。
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.system"></a>1.3.8. 系统变量</h3></div></div></div>
		<p>系统变量</p>
		<pre class="screen">
Shell常用的系统变量并不多，但却十分有用，特别是在做一些参数检测的时候。下面是Shell常用的系统变量
$n	 $1 表示第一个参数，$2 表示第二个参数 ...
$#	 命令行参数的个数
$0	 当前程序的名称
$?	 前一个命令或函数的返回码
$*	 以"参数1 参数2 ... " 形式保存所有参数
$@	 以"参数1" "参数2" ... 形式保存所有参数
$$	 本程序的(进程ID号)PID
$!	 上一个命令的PID
		<pre class="screen">
[root@cc tmp]# cat test.sh
[root@cc tmp]# ./test.sh  helloworld
		<pre class="screen">
其中使用得比较多得是 $n $# $0 $? ,看看下面的例子：
if [ $# -ne 2 ] ; then
echo "Usage: $0 string file";
grep $1 $2 ;
if [ $? -ne 0 ] ; then
echo "Not Found \"$1\" in $2";
echo "Found \"$1\" in $2";
上面的例子中使用了$0 $1 $2 $# $? 等变量
./chapter2.2.sh usage chapter2.2.sh
Not Found "usage" in chapter2.2.sh
-bash-2.05b$ ./chapter2.2.sh Usage chapter2.2.sh
echo "Usage: $0 string file";
Found "Usage" in chapter2.2.sh
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.number"></a>1.3.9. Numerical 数值运算</h3></div></div></div>
		<p>数值运算表达式</p>
		<pre class="screen">
$((EXPR))		
		<pre class="screen">
echo $((1+1))
echo $((5*5))
		<pre class="screen">
num=$(awk "BEGIN {print $num1+$num2; exit}")
num=$(python -c "print $num1+$num2")
num=$(perl -e "print $num1+$num2")
num=$(echo $num1 + $num2 | bc) 		
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.strings"></a>1.3.10. Strings 字符串操作</h3></div></div></div>
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931726752"></a>1.3.10.1. ##/#</h4></div></div></div>
			<pre class="screen">
$ MYVAR=foodforthought.jpg
$ echo ${MYVAR##*fo}
rthought.jpg
$ echo ${MYVAR#*fo}
odforthought.jpg
			<p>一个简单的脚本例子</p>
			<pre class="screen">
#!/bin/bash
if [ "${1##*.}" = "tar" ]
    echo This appears to be a tarball.
    echo At first glance, this does not appear to be a tarball.
$ ./mytar.sh thisfile.tar
This appears to be a tarball.
$ ./mytar.sh thatfile.gz
At first glance, this does not appear to be a tarball.
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931724272"></a>1.3.10.2. %%/%</h4></div></div></div>
			<pre class="screen">
$ MYFOO="chickensoup.tar.gz"
$ echo ${MYFOO%%.*}
chickensoup
$ echo ${MYFOO%.*}
chickensoup.tar
MYFOOD="chickensoup"
$ echo ${MYFOOD%%soup}
			<pre class="screen">
$ test="aaa bbb ccc ddd"
$ echo ${test% *}
aaa bbb ccc
$ echo ${test%% *}
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931722288"></a>1.3.10.3. :n1:n2</h4></div></div></div>
			<p>：${varible:n1:n2}:截取变量varible从n1到n2之间的字符串。</p>
			<pre class="screen">
$ EXCLAIM=cowabunga
$ echo ${EXCLAIM:0:3}
$ echo ${EXCLAIM:3:7}
file=netkiller.rpm
$echo ${file: -3}
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931720336"></a>1.3.10.4. #</h4></div></div></div>
			<p>：${varible:n1:n2}:截取变量varible从n1到n2之间的字符串。</p>
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931718944"></a>1.3.10.5. example</h4></div></div></div>
			<pre class="screen">
$cat name.sh
#!/bin/bash
while read line ; do
	fistname=${line% *}
	lastname=${line#* }
	echo $fistname $lastname
done &lt;&lt;EOF
$ bash name.sh
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="string.len"></a>1.3.10.6. 计算字符串长度</h4></div></div></div>
    		<p>计算字符串长度</p>
    		<pre class="screen">
echo ${#PATH}
    		</pre>
    	</div>
    	<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931715168"></a>1.3.10.7. 字符串查找替换</h4></div></div></div>
    		<pre class="screen">
# str="1 2 3 4";echo ${str// /}
# str="1 2 3 4";echo ${str// /,}
# str="1 2 3 4";echo ${str// /+}
# str="neo netkiller";echo ${str//neo/hello}
hello netkiller
    		</pre>
    	</div>
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="variable.array"></a>1.3.11. Array 数组</h3></div></div></div>
		<p>定义数组</p>
		<pre class="screen">
arr=(Hello World)
arr[0]=Hello
arr[1]=World
		<p>访问数组</p>
		<pre class="screen">
echo ${arr[0]} ${arr[1]}
${arr[*]}         # All of the items in the array
${!arr[*]}        # All of the indexes in the array
${#arr[*]}        # Number of items in the array
${#arr[0]}        # Length of item zero
		<p>追加操作</p>
		<pre class="screen">
ARRAY+=('foo')
ARRAY+=('bar')
		<pre class="screen">
#!/bin/bash
array=(one two three four [5]=five)
echo "Array size: ${#array[*]}"
echo "Array items:"
for item in ${array[*]}
    printf "   %s\n" $item
echo "Array indexes:"
for index in ${!array[*]}
    printf "   %d\n" $index
echo "Array items and indexes:"
for index in ${!array[*]}
    printf "%4d: %s\n" $index ${array[$index]}
		<pre class="screen">
#!/bin/bash
array=("first item" "second item" "third" "item")
echo "Number of items in original array: ${#array[*]}"
for ix in ${!array[*]}
    printf "   %s\n" "${array[$ix]}"
arr=(${array[*]})
echo "After unquoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
    printf "   %s\n" "${arr[$ix]}"
arr=("${array[*]}")
echo "After * quoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
    printf "   %s\n" "${arr[$ix]}"
arr=("${array[@]}")
echo "After @ quoted expansion: ${#arr[*]}"
for ix in ${!arr[*]}
    printf "   %s\n" "${arr[$ix]}"
		<pre class="screen">
array=({23..32} {49,50} {81..92})
echo "Array size: ${#array[*]}"
echo "Array items:"
for item in ${array[*]}
    printf "   %s\n" $item
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931706912"></a>1.3.11.1. 拆分字符串并转换为数组</h4></div><div><h5 class="subtitle">Split string into an array in Bash</h5></div></div></div>
			<p>字符串</p>
			<pre class="screen">
QUEUES="example|sss"			
			<p>类似列表的数据结构</p>
			<pre class="screen">
for caption in $(echo $QUEUES | tr '|' ' '); do 
        echo $caption
			<p>拆分为数组形式</p>
			<pre class="screen">
captions=($(echo $QUEUES | tr '|' ' '))
for element in "${captions[@]}"
    echo "$element"
for key in ${!captions[@]}; do
    echo ${key} ${captions[${key}]}
		<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm45249931702864"></a>1.3.11.2. 数组转为字符串</h4></div></div></div>
			<pre class="screen">
ids=(1 2 3 4);echo ${ids[*]// /|}
ids=(1 2 3 4); lst=$( IFS='|'; echo "${ids[*]}" ); echo $lst
array=(1 2 3 4); echo ${array[*]// /|}
array=(1 2 3 4);string="${ids[@]}";echo ${string// /|}
array=(1 2 3 4);string="${ids[@]}";echo ${string// /,}
IFS='|';echo "${[*]// /|}";
	<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="eval"></a>1.3.12. eval</h3></div></div></div>
		<pre class="screen">
$ eval echo $"a_$i"
		<pre class="screen">
# neo="Neo Chen"
# eval "echo \$$name"
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