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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>1.5. Loops for, while and until</title><link rel="stylesheet" type="text/css" href="..//docbook.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><meta name="keywords" content="shell,bash,zsh, awk,sed,curl,expect, grep,sort" /><link rel="home" href="../index.html" title="Netkiller Linux Shell 手札" /><link rel="up" href="index.html" title="第 1 章 Bash Shell" /><link rel="prev" href="conditions.html" title="1.4. conditions if and case" /><link rel="next" href="functions.html" title="1.6. Functions" /></head><body><a xmlns="" href="http://www.netkiller.cn/">Home</a> |
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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">1.5. Loops for, while and until</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="conditions.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="functions.html">下一页</a></td></tr></table><hr /></div><table xmlns=""><tr><td><iframe src="http://ghbtns.com/github-btn.html?user=netkiller&repo=netkiller.github.io&type=watch&count=true&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&repo=netkiller.github.io&type=fork&count=true&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&type=follow&count=true&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="loop"></a>1.5. Loops for, while and until</h2></div></div></div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="for"></a>1.5.1. for</h3></div></div></div>
<pre class="programlisting">
#!/bin/bash
for i in 1 2 3 4 5
do
echo "Welcome $i times"
done
for i in $( ls ); do
echo item: $i
done
for i in `seq 1 10`;
do
echo $i
done
for i in {1..5}
do
echo "Welcome $i times"
done
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times..."
done
for ((i=1; $i<=9;i++)); do echo $i; done
</pre>
<pre class="programlisting">
for i in {0..10..2}
do
echo "Welcome $i times"
done
for i in $(seq 1 2 20)
do
echo "Welcome $i times"
done
</pre>
<p>单行实例</p>
<pre class="programlisting">
for ip in {1..10};do echo $ip; done
for i in `seq 1 10`;do echo $i;done
for ip in {81..92}; do ssh root@172.16.3.$ip date; done
for n in {23..32} {49,50} {81..92}; do mkdir /tmp/$n; echo $n; done
</pre>
<p>infinite loops</p>
<pre class="programlisting">
#!/bin/bash
for (( ; ; ))
do
echo "infinite loops [ hit CTRL+C to stop]"
done
</pre>
<p>find file</p>
<pre class="programlisting">
#!/bin/bash
for file in /etc/*
do
if [ "${file}" == "/etc/resolv.conf" ]
then
countNameservers=$(grep -c nameserver /etc/resolv.conf)
echo "Total ${countNameservers} nameservers defined in ${file}"
break
fi
done
</pre>
<p>backup file</p>
<pre class="programlisting">
#!/bin/bash
FILES="$@"
for f in $FILES
do
# if .bak backup file exists, read next file
if [ -f ${f}.bak ]
then
echo "Skiping $f file..."
continue # read next file and skip cp command
fi
# we are hear means no backup file exists, just use cp command to copy file
/bin/cp $f $f.bak
done
</pre>
<pre class="screen">
for n in {23..32} {49,50} {81..92}; do mkdir /tmp/$n; echo $n; done
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="while"></a>1.5.2. while</h3></div></div></div>
<pre class="programlisting">
#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 10 ]; do
echo The counter is $COUNTER
let COUNTER=COUNTER+1
done
</pre>
<pre class="programlisting">
while read name age
do
echo $name $age
done << EOF
neo 30
jam 31
john 29
EOF
while read name age
do
[[ $age -gt 30 ]] && echo $name
done << EOF
neo 30
jam 31
john 29
EOF
</pre>
<pre class="programlisting">
$ cat mount.sh
#!/bin/sh
while read LINE
do
s=`echo $LINE|awk '{print $1}'`
d=`echo $LINE|awk '{print $2}'`
umount -f $d
mount -t nfs4 $s $d
done < mount.conf
$ cat mount.conf
172.16.0.1:/ /www/logs/1
172.16.0.2:/ /www/logs/2
172.16.0.3:/ /www/logs/3
172.16.0.4:/ /www/logs/4
172.16.0.5:/ /www/logs/5
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="until"></a>1.5.3. until</h3></div></div></div>
<pre class="programlisting">
#!/bin/bash
COUNTER=20
until [ $COUNTER -lt 10 ]; do
echo COUNTER $COUNTER
let COUNTER-=1
done
</pre>
</div>
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