bash
优质
小牛编辑
132浏览
2023-12-01
语法
基本语法
| 名称 | 语法 | 描述 | 示例 |
|---|---|---|---|
interpreter | #!/bin/bash | Bash shell 脚本的第一行以 #! 开头，通常也称为 sharp-bang 或缩写版本 sha-bang。后面的路径名称是命令解释器，也就是应该用于执行脚本的程序。 | |
echo | echo "arbitrary text" echo "arbitrary text" >&2 | 文本定向到标准输出 (STDOUT), 输出重定向将其定向到标准错误 (STDERR) | $ cat hello #!/bin/bash echo "Hello, world" echo "ERROR: Houston, we have a problem." >&2 $ ./hello 2> hello.log Hello, world $ cat hello.log ERROR: Houston, we have a problem. |
特殊字符 | \ '' "" `` | 处理特殊字符 | $ echo \# not a comment # not a comment $ echo '$HOME' $HOME $ echo "$HOME" /home/kylin $ echo `pwd` /home/kylin/tmp $ echo "\`pwd\`" `pwd` |
变量 | VARIABLENAME=value | 变量名称由数字、字母（大写和小写）和下划线字符 _ 组成，不能以数字开头，等号 = 用于为变量分配值，并且不能用空格将其与变量名称或值分隔开。 | COUNT=40 first_name=John file1=/tmp/abc _ID=RH123 full_name='John Doe' full_name="$FIRST $LAST" price='$1' |
变量扩展 | $VARIABLENAME
${VARIABLENAME} | 通过在变量名称前面加上美元符号 $，可以通过称为变量扩展的过程来重新调用变量的值。 | $ FIRST_=Jane
$ FIRST=John
$ LAST=Doe
$ echo $FIRST_$LAST
JaneDoe
$ echo ${FIRST}_$LAST
John_Doe |
命令替换 | `<COMMAND>` $(<COMMAND>) | 将命令的调用替换为执行命令后的输出 | $ echo "Current time: `date`" Current time: Tue May 1 10:44:51 CST 2018 $ echo "Current time: $(date)" Current time: Tue May 1 10:44:59 CST 2018 |
算术扩展 | $[<EXPRESSION>] | 执行简单的整数算术运算 | $ echo $[1+1] 2 $ echo $[2*2] 4 $ COUNT=1; echo $[$[$COUNT+1]*2] 4 $ SEC_PER_MIN=60 $ MIN_PER_HR=60 $ HR_PER_DAY=24 $ SEC_PER_DAY=$[$SEC_PER_MIN * $MIN_PER_HR * $HR_PER_DAY] $ echo "There are $SEC_PER_DAY seconds in a day." There are 86400 seconds in a day. |
for loop | for <VARIABLE> in <LIST>; do
<COMMAND>
...
<COMMAND> referencing <VARIABLE>
done | 循环按顺序逐一处理 <LIST> 中提供的项目，并且在处理列表中的最后一个项目之后退出。列表中的每个项目临时存储为 <VARIABLE> 的值，而 for 循环执行包含在其结构中的命令块。变量的命名是任意的。 | $ for HOST in host1 host2 host3; do echo $HOST; done
host1
host2
host3
$ for HOST in host{1,2,3}; do echo $HOST; done
host1
host2
host3
$ for HOST in host{1..3}; do echo $HOST; done
host1
host2
host3 |
传入参数 | $1, $2, $*, $@ | 将命令行参数的值存储到脚本中, 以数字方式对变量进行命名 | $ cat showargs #!/bin/bash for ARG in "$*"; do echo $ARG done $ ./showargs 1 2 3 1 2 3 |
退出代码 | $? | 每个命令返回一个退出状态，也通常称为返回状态或退出代码 | $ cat hello #!/bin/bash echo "Hello, world" exit 0 $ ./hello Hello, world $ echo $? 0 |
比较 | [ <ITEM1> <BINARY COMPARISON OPERATOR> <ITEM2> ] [ <UNARY OPERATOR> <ITEM> ] | 整数比较, 字符串比较，文件比较 | |
If/then | if <CONDITION>; then <STATEMENT> ... <STATEMENT> fi | 如果满足给定条件，将采取一个或多个操作。如果不满足给定条件，则不采取任何操作 | systemctl is-active psacct > /dev/null 2>&1 if [ $? -ne 0 ]; then systemctl start psacct fi |
If/then/else | if <CONDITION>; then
<STATEMENT>
...
<STATEMENT>
else
<STATEMENT>
...
<STATEMENT>
fi | if/then 条件结构可以进一步扩展，以便能够根据是否满足条件来采取不同的操作集合 | systemctl is-active psacct > /dev/null 2>&1 if [ $? -ne 0 ]; then systemctl start psacct else systemctl stop psacct fi |
If/then/elif/then/else | if <CONDITION>; then
<STATEMENT>
...
<STATEMENT>
elif <CONDITION>; then
<STATEMENT>
...
<STATEMENT>
else
<STATEMENT>
...
<STATEMENT>
fi | 测试多个条件 | systemctl is-active mariadb > /dev/null 2>&1 MARIADB_ACTIVE=$? systemctl is-active postgresql > /dev/null 2>&1 POSTGRESQL_ACTIVE=$? if [ "$MARIADB_ACTIVE" -eq 0 ]; then mysql elif [ "$POSTGRESQL_ACTIVE" -eq 0 ]; then psql else sqlite3 fi |
case | case <VALUE> in
<PATTERN1>)
<STATEMENT>
...
<STATEMENT>
;;
<PATTERN2>)
<STATEMENT>
...
<STATEMENT>
;;
esac | case 语句尝试按顺序逐个将 <VALUE> 与每个 <PATTERN> 进行匹配。当某个模式匹配时，将执行与该模式相关联的代码段，以 ;; 语法指示块的结束。 | case "$1" in
start)
start
;;
stop)
rm -f $lockfile
stop
;;
restart)
restart
;;
reload)
reload
;;
status)
status
;;
*)
echo "Usage: $0 (start |
stop | restart | reload | status)" ;; esac |
运算符及其含义
| 运算符 | 含义 |
|---|---|
<VARIABLE>++ | 变量后置递增 |
<VARIABLE>-- | 变量后置递减 |
++<VARIABLE> | 变量前置递增 |
--<VARIABLE> | 变量前置递减 |
- | 一元减法 |
+ | 一元加法 |
** | 求幂 |
* | 乘法 |
/ | 除法 |
% | 求余 |
+ | 加法 |
- | 减法 |
算术运算符优先级顺序
| 运算符 | 含义 |
|---|---|
<VARIABLE>++、<VARIABLE>-- | 变量后置递增和后置递减 |
++<VARIABLE>、--<VARIABLE> | 变量前置递增和前置递减 |
-、+ | 一元减法和加法 |
** | 求幂 |
*、/、% | 乘法、除法、求余 |
+、 - | 加法、减法 |
比较运算符
| 作用域 | 运算符 | 含义 | 示例 |
|---|---|---|---|
整数 | -eq | 等于 | [ "$a" -eq "$b" ] |
整数 | -ne | 不等于 | [ "$a" -ne "$b" ] |
整数 | -gt | 大于 | [ "$a" -gt "$b" ] |
整数 | -ge | 大于等于 | [ "$a" -ge "$b" ] |
整数 | -lt | 小于 | [ "$a" -lt "$b" ] |
整数 | -le | 小于等于 | [ "$a" -le "$b" ] |
字符串 | = | 等于 | [ "$a" = "$b" ] |
字符串 | == | 等于 | [ "$a" == "$b" ] |
字符串 | != | 不等于 | [ "$a" != "$b" ] |
字符串 | -z | 字符串的长度为零（空） | [ -z "$a" ] |
字符串 | -n | 字符串不为空 | [ -n "$a" ] |
文件 | -b | 文件存在并且是块特殊 | [ -b <FILE> ] |
文件 | -c | 文件存在并且是字符特殊 | [ -c <FILE> ] |
文件 | -d | 文件存在并且是目录 | [ -d <DIRECTORY> ] |
文件 | -e | 文件存在 | [ -e <FILE> ] |
文件 | -f | 文件是常规文件 | [ -f <FILE> ] |
文件 | -L | 文件存在并且是符号链接 | [ -L <FILE> ] |
文件 | -r | 文件存在并且授予了读权限 | [ -r <FILE> ] |
文件 | -s | 文件存在并且大小大于零 | [ -s <FILE> ] |
文件 | -w | 文件存在并且授予了写权限 | [ -w <FILE> ] |
文件 | -x | 文件存在并且授予了执行（或搜索）权限 | [ -x <FILE> ] |
文件 | -ef | FILE1 与 FILE2 的设备和索引节点编号相同 | [ <FILE1> -ef <FILE2> ] |
文件 | -nt | FILE1 的修改日期比 FILE2 晚 | [ <FILE1> -nt <FILE2> ] |
文件 | -ot | FILE1 的修改日期比 FILE2 早 | [ <FILE1> -ot <FILE2> ] |
示例
提供 kernel 相关包信息
#!/bin/bash
#
# This script provides information regarding when kernel-related packages
# are installed on a system by querying information from the RPM database.
#
# Variables
PACKAGETYPE=kernel
PACKAGES=$(rpm -qa | grep $PACKAGETYPE)
# Loop through packages
for PACKAGE in $PACKAGES; do
# Determine package install date and time
INSTALLEPOCH=$(rpm -q --qf "%{INSTALLTIME}\n" $PACKAGE)
# RPM reports time in epoch, so need to convert
# it to date and time format with date command
INSTALLDATETIME=$(date -d @$INSTALLEPOCH)
# Print message
echo "$PACKAGE was installed on $INSTALLDATETIME"
doneMariaDB 数据备份
创建数据库备份目录mkdir /dbbackup$ mysql --skip-column-names -E -uroot -predhat -e 'SHOW DATABASES' | grep -v '^*' | grep -v '^information_schema$' | grep -v '^performance_schema$'
JDGCACHESTORE
apaccustomers
brokerinfo
eucustomers
matdb
mysql
products
test
uscustomers#!/bin/bash
# Variables
DBUSER=root
DBPASSWORD=redhat
FMTOPTIONS='--skip-column-names -E'
COMMAND='SHOW DATABASES'
BACKUPDIR=/dbbackup
# Backup non-system databases
for DBNAME in $(mysql $FMTOPTIONS -u$DBUSER -p$DBPASSWORD -e "$COMMAND" | grep -v ^* | grep -v information_schema | grep -v performance_schema); do
echo "Backing up \"$DBNAME\""
mysqldump -u$DBUSER -p$DBPASSWORD $DBNAME > $BACKUPDIR/$DBNAME.dump
done
# Add up size of all database dumps
for DBDUMP in $BACKUPDIR/*; do
SIZE=$(stat --printf "%s\n" $DBDUMP)
TOTAL=$[ $TOTAL + $SIZE ]
done
# Report name, size, and percentage of total for each database dump
echo
for DBDUMP in $BACKUPDIR/*; do
SIZE=$(stat --printf "%s\n" $DBDUMP)
echo "$DBDUMP,$SIZE,$[ 100 * $SIZE / $TOTAL ]%"
done$ dbbackup
Backing up "JDGCACHESTORE"
Backing up "apaccustomers"
Backing up "brokerinfo"
Backing up "eucustomers"
Backing up "matdb"
Backing up "mysql"
Backing up "products"
Backing up "test"
Backing up "uscustomers"
/dbbackup/apaccustomers.dump,7851,1%
/dbbackup/brokerinfo.dump,3239,0%
/dbbackup/eucustomers.dump,9697,1%
/dbbackup/JDGCACHESTORE.dump,4083,0%
/dbbackup/matdb.dump,7275,1%
/dbbackup/mysql.dump,514266,89%
/dbbackup/products.dump,15940,2%
/dbbackup/test.dump,3929,0%
/dbbackup/uscustomers.dump,9928,1%传入参数
#!/bin/bash
echo "$0 has $# arguments."
# Optionally, use 'for ARG in "$*"; do' will output the arguments in one line
for ARG in "$@"; do
echo $ARG
done$ ./showargs foo bar zoo
./showargs has 3 arguments.
foo
bar
zoo比较运算符
#!/bin/bash
[ 1 -eq 1 ]; echo $?;
[ 1 -ne 1 ]; echo $?;
[ 8 -gt 2 ]; echo $?;
[ 2 -ge 2 ]; echo $?;
[ 2 -lt 2 ]; echo $?;
[ 1 -lt 2 ]; echo $?;
[ abc = abc ]; echo $?;
[ abc == def ]; echo $?;
[ abc != def ]; echo $?;
STRING=''; [ -z "$STRING" ]; echo $?;
STRING='abc'; [ -n "$STRING" ]; echo $?;
[ 2 -gt 1 ] && [ 1 -gt 0 ]; echo $?;
[ 2 -gt 1 ] && [ 1 -gt 2 ]; echo $?;
[ 2 -gt 1 ] || [ 1 -gt 2 ]; echo $?;
[ 0 -gt 1 ] || [ 1 -gt 2 ]; echo $?;创建 httpd 虚拟主机
#!/bin/bash
# Variables
VHOSTNAME=$1
TIER=$2
HTTPDCONF=/etc/httpd/conf/httpd.conf
VHOSTCONFDIR=/etc/httpd/conf.vhosts.d
DEFVHOSTCONFFILE=$VHOSTCONFDIR/00-default-vhost.conf
VHOSTCONFFILE=$VHOSTCONFDIR/$VHOSTNAME.conf
WWWROOT=/srv
DEFVHOSTDOCROOT=$WWWROOT/default/www
VHOSTDOCROOT=$WWWROOT/$VHOSTNAME/www
# Check arguments
if [ "$VHOSTNAME" = '' ] || [ "$TIER" = '' ]; then
echo "Usage: $0 VHOSTNAME TIER"
exit 1
else
case $TIER in
1) VHOSTADMIN='basic_support@example.com'
;;
2) VHOSTADMIN='business_support@example.com'
;;
3) VHOSTADMIN='enterprise_support@example.com'
;;
*) echo "Invalid tier specified."
exit 1
;;
esac
fi
# Create conf directory one time if non-existent
if [ ! -d $VHOSTCONFDIR ]; then
mkdir $VHOSTCONFDIR
if [ $? -ne 0 ]; then
echo "ERROR: Failed creating $VHOSTCONFDIR."
exit 1
fi
fi
# Add include one time if missing
grep -q '^IncludeOptional conf\.vhosts\.d/\*\.conf$' $HTTPDCONF
if [ $? -ne 0 ]; then
# Backup before modifying
cp -a $HTTPDCONF $HTTPDCONF.orig
echo "IncludeOptional conf.vhosts.d/*.conf" >> $HTTPDCONF
if [ $? -ne 0 ]; then
echo "ERROR: Failed adding include directive."
exit 1
fi
fi
cat <<DEFCONFEOF > $DEFVHOSTCONFFILE
<VirtualHost _default_:80>
DocumentRoot $DEFVHOSTDOCROOT
CustomLog "logs/default-vhost.log" combined
</VirtualHost>
<Directory $DEFVHOSTDOCROOT>
Require all granted
</Directory>
DEFCONFEOF
# Check for default virtual host
if [ ! -f $DEFVHOSTCONFFILE ]; then
cat <<DEFCONFEOF > $DEFVHOSTCONFFILE
<VirtualHost _default_:80>
DocumentRoot $DEFVHOSTDOCROOT
CustomLog "logs/default-vhost.log" combined
</VirtualHost>
<Directory $DEFVHOSTDOCROOT>
Require all granted
</Directory>
DEFCONFEOF
fi
if [ ! -d $DEFVHOSTDOCROOT ]; then
mkdir -p $DEFVHOSTDOCROOT
restorecon -Rv /srv/
fi
cat <<CONFEOF > $VHOSTCONFFILE
<VirtualHost *:80>
ServerName $VHOSTNAME
ServerAdmin $VHOSTADMIN
DocumentRoot $VHOSTDOCROOT
ErrorLog "logs/${VHOSTNAME}_error_log"
CustomLog "logs/${VHOSTNAME}_access_log" common
</VirtualHost>
<Directory $VHOSTDOCROOT>
Require all granted
</Directory>
CONFEOF
# Check for virtual host conflict
if [ -f $VHOSTCONFFILE ]; then
echo "ERROR: $VHOSTCONFFILE already exists."
exit 1
elif [ -d $VHOSTDOCROOT ]; then
echo "ERROR: $VHOSTDOCROOT already exists."
exit 1
else
cat <<CONFEOF > $VHOSTCONFFILE
<Directory $VHOSTDOCROOT>
Require all granted
AllowOverride None
</Directory>
<VirtualHost *:80>
DocumentRoot $VHOSTDOCROOT
ServerName $VHOSTNAME
ServerAdmin $VHOSTADMIN
ErrorLog "logs/${VHOSTNAME}_error_log"
CustomLog "logs/${VHOSTNAME}_access_log" common
</VirtualHost>
CONFEOF
mkdir -p $VHOSTDOCROOT
restorecon -Rv $WWWROOT
fi
# Check config and reload
apachectl configtest &> /dev/null
if [ $? -eq 0 ]; then
systemctl reload httpd &> /dev/null
else
echo "ERROR: Config error."
exit 1
fimkvhost test.example.com 2export 对比实验
| 不使用 export | 使用 export |
|---|---|
| |
批量创建 Linux 用户
在 server0 上创建一个脚本，名为 /root/mkusers , 同时满足下列要求：
此脚本能实现为系统 server0 创建本地用户, 这些用户的用户名来自一个包含用户名列表的文件
此脚本要求提供一个参数，此参数就是包含用户名列表的文件
如果没有提供参数，此脚本应该给出下面的提示信息 Usage: /root/mkusers <userfile> 然后退出并返回相应的值
如果提供一个不存在的文件名，此脚本应该给出下面的提示信息 Input file not found 然后退出并返回相应的值
创建的用户登录 shell 为 /bin/false
此脚本不需要为用户设置密码
# for i in tom jerry alias natasha mario harry ; do echo $i >> sample.users ; done
# cat sample.users
tom
jerry
alias
natasha
mario
harry#!/bin/bash
if [ $# -ne 1 ]; then
echo 'Usage: /root/makeusers <userfile>'
exit 1
fi
if [ ! -f "$1" ]; then
echo "Input file not found"
exit 2
fi
while read line
do useradd -s /bin/false $line
done < $1# chmod +x makeusers
# ./makeusers
Usage: /root/makeusers <userfile>
# ./makeusers no.exsit
Input file not found
# ./makeusers sample.users && tail -n 6 /etc/passwd
tom:x:1001:1001::/home/tom:/bin/false
jerry:x:1002:1002::/home/jerry:/bin/false
alias:x:1003:1003::/home/alias:/bin/false
natasha:x:1004:1004::/home/natasha:/bin/false
mario:x:1005:1005::/home/mario:/bin/false
harry:x:1006:1006::/home/harry:/bin/falsecase/switch 示例
在 server0 上创建一个名为 /root/script.sh 的脚本， 让其提供下列特性：
当运行 /root/script.sh all，输出为 none
当运行 /root/script.sh none，输出为 all
当没有任何参数或者参数不是 all 或者 none时， 其错误输出产生以下的信息：all|none
#!/bin/bash
case $1 in
all)
echo "none" ;;
none)
echo "all" ;;
*)
echo "all|none" ;;
esac# chmod +x script.sh
# /root/script.sh all
none
# /root/script.sh none
all
# /root/script.sh
all|none
# /root/script.sh xxx
all|none