# 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 ```