在centos系统shell脚本中cat和重定向符号<<EOF结合使用的注意事项

在运维人员编写shell脚本中，有时会需要将一些内容直接放在到一个文件，比如在一个shell脚本中配置一些内容再生成一个shell脚本，此时可以使用到cat命令和重定向符号“<<”以及EOF的使用。但是，在shell脚本中使用重定向符号生成shell脚本时，会遇到一些问题，比如，内容中含有特殊符号"#","`","$"时，（如果以“#”开头，则需要加转义符“\”）重定向会忽略这些特殊符号，而导致生成的shell脚本无法运行，此时只需要在这些特殊符号前加转义符号“\”即可，如下是一个自动安装nginx的脚本：

#!/bin/sh
#the script is install nginx
#echo "add user mars"
#groupadd xiaoyao && useradd -g xiaoyao xiaoyao && sed -i 's/\#PermitRootLogin yes/PermitRootLogin no/g' /etc/ssh/sshd_config && service sshd restart && passwd xiaoyao
echo "configure sysctl"
mv /etc/sysctl.conf /etc/sysctl.conf.bak
cat >>/etc/sysctl.conf<<EOF
net.ipv4.ip_forward = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies = 1
kernel.msgmnb = 65536
kernel.msgmax = 65536
kernel.shmmax = 68719476736
kernel.shmall = 4294967296
net.ipv4.tcp_max_tw_buckets = 6000
net.ipv4.tcp_sack = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_rmem = 4096 87380 4194304
net.ipv4.tcp_wmem = 4096 16384 4194304
net.core.wmem_default = 8388608
net.core.rmem_default = 8388608
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.netdev_max_backlog = 262144
net.core.somaxconn = 262144
net.ipv4.tcp_max_orphans = 3276800
net.ipv4.tcp_max_syn_backlog = 262144
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_syn_retries = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_mem = 94500000 915000000 927000000
net.ipv4.tcp_fin_timeout = 1
net.ipv4.tcp_keepalive_time = 30
net.ipv4.ip_local_port_range = 1024 65000
EOF

sysctl -p
echo "configure sysctl is complete!"

yum install -y gcc gcc-c++ openssl openssl-devel pcre-devel
cd /data/tools
tar -zxvf pcre-8.37.tar.gz -C /usr/local/src/
cd /usr/local/src/pcre-8.37/
./configure --prefix=/usr/local/pcre
make &&make install
cd /data/tools
tar -zxvf libevent-2.0.22-stable.tar.gz -C /usr/local/src/
cd /usr/local/src/libevent-2.0.22-stable/
./configure --prefix=/usr/local/libevent
make && make install
cd /usr/local/libevent/
ln -s /usr/local/libevent/include /usr/include/libevent
echo "/usr/local/libevent/lib" >>/etc/ld.so.conf.d/libevent.conf
ldconfig -pv | grep libevent
groupadd nginx
useradd -r -g nginx -s /sbin/nologin -M nginx
cd /data/tools
tar -zxvf nginx-1.8.0.tar.gz -C /usr/local/src/
cd /usr/local/src/nginx-1.8.0/
./configure \
--conf-path=/etc/nginx/nginx.conf  \
--error-log-path=/var/log/nginx/error.log \
--http-log-path=/var/log/nginx/access.log \
--pid-path=/var/run/nginx.pid  \
--lock-path=/var/lock/nginx.lock  \
--user=nginx  \
--group=nginx  \
--with-http_ssl_module \
--with-http_flv_module \
--with-http_stub_status_module \
--with-http_gzip_static_module \
--http-client-body-temp-path=/var/tmp/nginx/client/ \
--http-proxy-temp-path=/var/tmp/nginx/proxy/ \
--http-fastcgi-temp-path=/var/tmp/nginx/fcgi/ \
--with-pcre=/usr/local/src/pcre-8.37
ln -s /var/log/nginx/error.log /etc/nginx/error.log
ln -s /var/log/nginx/access.log /etc/nginx/access.log
ln -s /var/run/nginx.pid /etc/nginx/nginx.pid
ln -s /var/lock/nginx.lock /etc/nginx/nginx.lock
make && make install
cd /usr/local/nginx
mkdir -pv /var/tmp/nginx/client
mkdir -pv /var/tmp/nginx/proxy
mkdir -pv /var/tmp/nginx/fcgi
echo "PATH=$PATH:/usr/local/nginx/sbin" >>/etc/profile
source /etc/profile
cat >>/etc/init.d/nginx<<EOF
\#!/bin/bash
\# chkconfig: 2345 65 45
\# description: nginx serverdaemon
prog=/usr/local/nginx/sbin/nginx
lockfile=/var/lock/nginx.lock
pidfile=/var/run/nginx.pid
start(){
#以下的$、`、#前都加了转义符号"\"
[ -f \$lockfile ] && echo"nginx is started." && exit
echo -n "nginx is starting.."
sleep 1 && echo -n"."
\$prog &&  echo -e  "\$space[\033[32m OK\033[0m]" && touch \$lockfile || echo  -e "\$space[\033[31m failed\033[0m]"
}
stop(){
[ ! -f \$lockfile ] && echo"nginx is stopped." && exit
echo -n "nginx is stopping.."
sleep 1 && echo -n"."
\$prog -s stop && echo  -e "\$space[\033[32m OK \033[0m]"&& rm -f \$lockfile || echo  -e"\$space[\033[31m failed \033[0m]"
}
status(){
[ ! -f \$pidfile ] && echo"nginx is stoped" || echo "\`cat \$pidfile\`,nginx is running"
}

case "\$1" in
start)
start
;;
stop)
stop
;;
restart)
stop
start
;;
status)
status
;;
*)
echo "UASGE IS:start|stop|restart|status"
;;
esac

EOF
#生成后，需要将“\#”修改会“#”，而“\`”及“\$”则会自动转为“`”以及“$”
sed -i 's/\\\#/\#/g' /etc/init.d/nginx
chmod  +x /etc/init.d/nginx
chkconfig --add nginx
chkconfig --list nginx
service nginx start
echo "suessfull!!"

通过以上操作，我们就很方便的在shell脚本中实现生成文件或者脚本了。

还有请注意，如“\”转义符不能同时有两个以上，否则也会无法写入。