363 lines
8.4 KiB
Markdown
363 lines
8.4 KiB
Markdown
# 原创
|
||
： Shell流程控制：case 分支
|
||
|
||
# Shell流程控制：case 分支
|
||
|
||
## 流程控制：case 分支
|
||
|
||
### case
|
||
|
||
```
|
||
case word in
|
||
[pattern [| pattern]...) commands ;;]...
|
||
esac
|
||
|
||
```
|
||
|
||
```
|
||
#!/bin/bash
|
||
# case-menu: a menu driven system information program
|
||
clear
|
||
echo "
|
||
Please Select:
|
||
1. Display System Information
|
||
2. Display Disk Space
|
||
3. Display Home Space Utilization
|
||
0. Quit
|
||
"
|
||
read -p "Enter selection [0-3] > "
|
||
case $REPLY in
|
||
0) echo "Program terminated."
|
||
exit
|
||
;;
|
||
1) echo "Hostname: $HOSTNAME"
|
||
uptime
|
||
;;
|
||
2) df -h
|
||
;;
|
||
3) if [[ $(id -u) -eq 0 ]]; then
|
||
echo "Home Space Utilization (All Users)"
|
||
du -sh /home/*
|
||
else
|
||
echo "Home Space Utilization ($USER)"
|
||
du -sh $HOME
|
||
fi
|
||
;;
|
||
*) echo "Invalid entry" >&2
|
||
exit 1
|
||
;;
|
||
esac
|
||
|
||
```
|
||
|
||
### 模式
|
||
|
||
case 语句使用的模式和路径展开中使用的那些是一样的。模式以一个 “)” 为终止符。这里是一些有效的模式。
|
||
|
||
|模式|描述
|
||
|------
|
||
|a)|若单词为 “a”，则匹配
|
||
|[[:alpha:]])|若单词是一个字母字符，则匹配
|
||
|???)|若单词只有3个字符，则匹配
|
||
|*.txt)|若单词以 “.txt” 字符结尾，则匹配
|
||
|*)|匹配任意单词。把这个模式做为 case 命令的最后一个模式，是一个很好的做法， 可以捕捉到任意一个与先前模式不匹配的数值；也就是说，捕捉到任何可能的无效值。
|
||
|
||
```
|
||
#!/bin/bash
|
||
read -p "enter word > "
|
||
case $REPLY in
|
||
[[:alpha:]]) echo "is a single alphabetic character." ;;
|
||
[ABC][0-9]) echo "is A, B, or C followed by a digit." ;;
|
||
???) echo "is three characters long." ;;
|
||
*.txt) echo "is a word ending in '.txt'" ;;
|
||
*) echo "is something else." ;;
|
||
esac
|
||
|
||
```
|
||
|
||
还可以使用竖线字符作为分隔符，把多个模式结合起来。这就创建了一个 “或” 条件模式。这对于处理诸如大小写字符很有用处。例如：
|
||
|
||
```
|
||
#!/bin/bash
|
||
# case-menu: a menu driven system information program
|
||
clear
|
||
echo "
|
||
Please Select:
|
||
A. Display System Information
|
||
B. Display Disk Space
|
||
C. Display Home Space Utilization
|
||
Q. Quit
|
||
"
|
||
read -p "Enter selection [A, B, C or Q] > "
|
||
case $REPLY in
|
||
q|Q) echo "Program terminated."
|
||
exit
|
||
;;
|
||
a|A) echo "Hostname: $HOSTNAME"
|
||
uptime
|
||
;;
|
||
b|B) df -h
|
||
;;
|
||
c|C) if [[ $(id -u) -eq 0 ]]; then
|
||
echo "Home Space Utilization (All Users)"
|
||
du -sh /home/*
|
||
else
|
||
echo "Home Space Utilization ($USER)"
|
||
du -sh $HOME
|
||
fi
|
||
;;
|
||
*) echo "Invalid entry" >&2
|
||
exit 1
|
||
;;
|
||
esac
|
||
|
||
```
|
||
|
||
添加的 “;;&” 的语法允许 case 语句继续执行下一条测试，而不是简单地终止运行。
|
||
|
||
```
|
||
|
||
#!/bin/bash
|
||
# case4-2: test a character
|
||
read -n 1 -p "Type a character > "
|
||
echo
|
||
case $REPLY in
|
||
[[:upper:]]) echo "'$REPLY' is upper case." ;;&
|
||
[[:lower:]]) echo "'$REPLY' is lower case." ;;&
|
||
[[:alpha:]]) echo "'$REPLY' is alphabetic." ;;&
|
||
[[:digit:]]) echo "'$REPLY' is a digit." ;;&
|
||
[[:graph:]]) echo "'$REPLY' is a visible character." ;;&
|
||
[[:punct:]]) echo "'$REPLY' is a punctuation symbol." ;;&
|
||
[[:space:]]) echo "'$REPLY' is a whitespace character." ;;&
|
||
[[:xdigit:]]) echo "'$REPLY' is a hexadecimal digit." ;;&
|
||
esac
|
||
|
||
```
|
||
|
||
## 位置参数
|
||
|
||
### 访问命令行
|
||
|
||
shell 提供了一个称为位置参数的变量集合，这个集合包含了命令行中所有独立的单词。这些变量按照从0到9给予命名。
|
||
|
||
```
|
||
#!/bin/bash
|
||
# posit-param: script to view command line parameters
|
||
echo "
|
||
\$0 = $0
|
||
\$1 = $1
|
||
\$2 = $2
|
||
\$3 = $3
|
||
\$4 = $4
|
||
\$5 = $5
|
||
\$6 = $6
|
||
\$7 = $7
|
||
\$8 = $8
|
||
\$9 = $9
|
||
"
|
||
|
||
```
|
||
|
||
```
|
||
[me@linuxbox ~]$ posit-param a b c d
|
||
$0 = /home/me/bin/posit-param
|
||
$1 = a
|
||
$2 = b
|
||
$3 = c
|
||
$4 = d
|
||
$5 =
|
||
$6 =
|
||
$7 =
|
||
$8 =
|
||
$9 =
|
||
|
||
```
|
||
|
||
### shift - 访问多个参数的利器
|
||
|
||
执行一次 shift 命令， 就会导致所有的位置参数 “向下移动一个位置”。
|
||
|
||
```
|
||
#!/bin/bash
|
||
# posit-param2: script to display all arguments
|
||
# 只要参数个数不为零就会继续执行的 while 循环
|
||
count=1
|
||
while [[ $# -gt 0 ]]; do
|
||
echo "Argument $count = $1"
|
||
count=$((count + 1))
|
||
shift
|
||
done
|
||
|
||
```
|
||
|
||
```
|
||
[me@linuxbox ~]$ posit-param2 a b c d
|
||
Argument 1 = a
|
||
Argument 2 = b
|
||
Argument 3 = c
|
||
Argument 4 = d
|
||
|
||
```
|
||
|
||
### 处理集体位置参数
|
||
|
||
shell 提供了两种特殊的参数，他们二者都能扩展成完整的位置参数列表，但以相当微妙的方式略有不同。
|
||
|
||
|参数|描述
|
||
|------
|
||
|$*|展开成一个从1开始的位置参数列表。当它被用双引号引起来的时候，展开成一个由双引号引起来 的字符串，包含了所有的位置参数，每个位置参数由 shell 变量 IFS 的第一个字符（默认为一个空格）分隔开。
|
||
|$@|展开成一个从1开始的位置参数列表。当它被用双引号引起来的时候， 它把每一个位置参数展开成一个由双引号引起来的分开的字符串。
|
||
|
||
```
|
||
#!/bin/bash
|
||
# posit-params3 : script to demonstrate $* and $@
|
||
print_params () {
|
||
echo "\$1 = $1"
|
||
echo "\$2 = $2"
|
||
echo "\$3 = $3"
|
||
echo "\$4 = $4"
|
||
}
|
||
pass_params () {
|
||
echo -e "\n" '$* :'; print_params $*
|
||
echo -e "\n" '"$*" :'; print_params "$*"
|
||
echo -e "\n" '$@ :'; print_params $@
|
||
echo -e "\n" '"$@" :'; print_params "$@"
|
||
}
|
||
pass_params "word" "words with spaces"
|
||
|
||
```
|
||
|
||
```
|
||
[me@linuxbox ~]$ posit-param3
|
||
$* :
|
||
$1 = word
|
||
$2 = words
|
||
$3 = with
|
||
$4 = spaces
|
||
"$*" :
|
||
$1 = word words with spaces
|
||
$2 =
|
||
$3 =
|
||
$4 =
|
||
$@ :
|
||
$1 = word
|
||
$2 = words
|
||
$3 = with
|
||
$4 = spaces
|
||
"$@" :
|
||
$1 = word
|
||
$2 = words with spaces
|
||
$3 =
|
||
$4 =
|
||
|
||
```
|
||
|
||
### 一个更复杂的应用
|
||
|
||
```
|
||
#!/bin/bash
|
||
# sys_info_page: program to output a system information page
|
||
PROGNAME=$(basename $0)
|
||
TITLE="System Information Report For $HOSTNAME"
|
||
CURRENT_TIME=$(date +"%x %r %Z")
|
||
TIMESTAMP="Generated $CURRENT_TIME, by $USER"
|
||
report_uptime () {
|
||
cat <<- _EOF_
|
||
<H2>System Uptime</H2>
|
||
<PRE>$(uptime)</PRE>
|
||
_EOF_
|
||
return
|
||
}
|
||
report_disk_space () {
|
||
cat <<- _EOF_
|
||
<H2>Disk Space Utilization</H2>
|
||
<PRE>$(df -h)</PRE>
|
||
_EOF_
|
||
return
|
||
}
|
||
report_home_space () {
|
||
if [[ $(id -u) -eq 0 ]]; then
|
||
cat <<- _EOF_
|
||
<H2>Home Space Utilization (All Users)</H2>
|
||
<PRE>$(du -sh /home/*)</PRE>
|
||
_EOF_
|
||
else
|
||
cat <<- _EOF_
|
||
<H2>Home Space Utilization ($USER)</H2>
|
||
<PRE>$(du -sh $HOME)</PRE>
|
||
_EOF_
|
||
fi
|
||
return
|
||
}
|
||
usage () {
|
||
echo "$PROGNAME: usage: $PROGNAME [-f file | -i]"
|
||
return
|
||
}
|
||
write_html_page () {
|
||
cat <<- _EOF_
|
||
<HTML>
|
||
<HEAD>
|
||
<TITLE>$TITLE</TITLE>
|
||
</HEAD>
|
||
<BODY>
|
||
<H1>$TITLE</H1>
|
||
<P>$TIMESTAMP</P>
|
||
$(report_uptime)
|
||
$(report_disk_space)
|
||
$(report_home_space)
|
||
</BODY>
|
||
</HTML>
|
||
_EOF_
|
||
return
|
||
}
|
||
# process command line options
|
||
interactive=
|
||
filename=
|
||
while [[ -n $1 ]]; do
|
||
case $1 in
|
||
-f | --file) shift
|
||
filename=$1
|
||
;;
|
||
-i | --interactive) interactive=1
|
||
;;
|
||
-h | --help) usage
|
||
exit
|
||
;;
|
||
*) usage >&2
|
||
exit 1
|
||
;;
|
||
esac
|
||
shift
|
||
done
|
||
# interactive mode
|
||
if [[ -n $interactive ]]; then
|
||
while true; do
|
||
read -p "Enter name of output file: " filename
|
||
if [[ -e $filename ]]; then
|
||
read -p "'$filename' exists. Overwrite? [y/n/q] > "
|
||
case $REPLY in
|
||
Y|y) break
|
||
;;
|
||
Q|q) echo "Program terminated."
|
||
exit
|
||
;;
|
||
*) continue
|
||
;;
|
||
esac
|
||
fi
|
||
done
|
||
fi
|
||
# output html page
|
||
if [[ -n $filename ]]; then
|
||
if touch $filename && [[ -f $filename ]]; then
|
||
write_html_page > $filename
|
||
else
|
||
echo "$PROGNAME: Cannot write file '$filename'" >&2
|
||
exit 1
|
||
fi
|
||
else
|
||
write_html_page
|
||
fi
|
||
|
||
```
|