shell实例(七) --参数/字符串替换

　　1.说明 ${parameter-default} --------如果变量parameter没被声明，那么就使用默认值
　　${parameter:-default} -------如果变量parameter没被设置，那么就使用默认值
　　filename=${1:-$DEFAULT_FILENAME}---------如果参数1没有设置，那么就取默认的DEFAULT_FILENAME
　　${parameter=default} ----如果变量parameter没声明，那么就把它的值设为default.
　　${parameter:=default} -----如果变量parameter没设置，那么就把它的值设为default. 
　　${parameter+alt_value} ----如果变量parameter被声明，那么就是用alt_value,否则使用null字符串.
　　${parameter:+alt_value} -----如果变量parameter被设置，那么就是用alt_value,否则使用null字符串. 
　　${parameter?err_msg} -----如果parameter已经被声明，那么就使用设置的值，否则打印err_msg错误消息.
　　${parameter:?err_msg} ----如果parameter已经被设置，那么就使用设置的值，否则打印err_msg错误消息.
　　冒号在linux中的使用
　　1、注释
　　: this is comment
　　: ' this is a multiple
　　lines comment.'
　　将注释作为参数传递给冒号命令， 因为没有输出所以可以当作注释阿，够巧妙吧。
　　2、清空文件
　　: > file
　　2.使用参数替换和错误消息
　　#! /bin/sh
　　: ${HOSTNAME?} ${USER?} ${HOME?} ${MAIL?}
　　echo
　　echo "Name of the machine is $HOSTNAME."
　　echo "You are $USER."
　　echo "Your home directory is $HOME."
　　echo "Your mail INBOX is located in $MAIL."
　　echo
　　echo "If you are reading this message,"
　　echo "critical environmental variables have been set."
　　echo
　　echo
　　ThisVariable=Value-of-ThisVariable
　　: ${ThisVariable?}
　　echo "Value of ThisVariable is $ThisVariable."
　　echo
　　echo
　　: ${ZZXy23AB?"ZZXy23AB has not been set."}
　　echo "You will not seen this message,because script already terminated."
　　HERE=0
　　exit $HERE
　　3.变量长度
　　${#array

}和${#array[@]}表示数组中元素的个数

　　#! /bin/sh
　　E_NO_ARGS=65
　　if [ $# -eq 0 ]
　　then
　　echo "Please invoke this script with one or two command-line arguments."
　　exit $E_NO_ARGS
　　fi
　　var01=abcdEFGH28ij
　　echo "var01 = ${var01}"
　　echo "Length of var01 = ${#var01}"
　　var02="abcd EFGH28ij"
　　echo "var01 = ${var02}"
　　echo "Length of var02 = ${#var02}"
　　echo "Number of command-line arguments passed to script = ${#@}" -----参数个数
　　echo "Number of command-line arguments passed to script = ${#*}"  -----参数个数
　　exit 0
　　4.参数替换中的模式匹配
　　#! /bin/sh
　　var1=abcd12345abc6789
　　pattern1=a*c
　　echo
　　echo "var1 = $var1"
　　echo "var1 = ${var1}"
　　echo "Number of characters in ${var1} = ${#var1}"
　　echo
　　echo "pattern1 = $pattern1"
　　echo "---------1--------"
　　echo '${var1#$pattern1} = ' "${var1#$pattern1}"
　　echo '${var##$pattern1} = ' "${var1##$pattern1}"
　　echo;echo;echo
　　pattern2=b*9
　　echo "var1 = $var1"
　　echo
　　echo "pattern2 = $pattern2"
　　echo "-------------------"
　　echo '${var1%pattern2} = ' "${var1%$pattern2}"
　　echo '${var1%%pattern2} = ' "${var1%%$pattern2}"
　　echo
　　exit 0
　　5.修改文件扩展名
　　#! /bin/sh
　　E_BADARGS=65
　　case $# in
　　0|1)
　　echo "Usage: `basename $0` old file suffix new file suffix"
　　exit $E_BADARGS
　　;;
　　esac
　　for filename in *.$1
　　do
　　mv $filename ${filename%$1}$2
　　done
　　exit 0
　　6.用模式匹配来解析任意字符串
　　#! /bin/sh
　　var1=abcd-1234-defg
　　echo "var1 = $var1"
　　t=${var1#*-*}
　　echo "var1 (with everything,up to and including first - strippedout) = $t"
　　t=${var1##*-*}
　　echo "If var1 contains a \"-\",returns empty string... var1=$t"
　　t=${var1%*-*}
　　echo "var1 (with everything from the last - on stripped out) = $t"
　　echo
　　path_name=/home/bozo/ideas/thoughts.for.today
　　echo "path_name=$path_name"
　　t=${path_name##/*/}  ------截去最大匹配/*/
　　echo "path_name,stripped of prefixes = $t"
　　t=${path_name%/*.*} ------从尾部截去/*.*
　　echo "path_name,stripped of suffixes = $t"
　　echo
　　t=${path_name:11}
　　echo "$path_name,with first 11 chars stripped of = $t"
　　t=${path_name:11:5}
　　echo "$path_name,with first 11 chars stripped off,length 5 = $t"
　　echo
　　t=${path_name/bozo/clown}
　　echo "$path_name with \"bozo\" replaced by \"clown\" = $t"
　　t=${path_name/today/}
　　echo "$path_name with \"today\" delete = $t"
　　t=${path_name//o/O}
　　echo "$path_name with all o's capitalized = $t"
　　t=${path_name//o/}
　　echo "$path_name with all o's deleted = $t"
　　exit 0
　　7.对字符串的前缀和后缀使用匹配模式
　　${var/#pattern/replacement}----如果变量var的前缀匹配pattern，那么就是用replacement来替换匹配到的pattern字符串
　　${var/%pattern/replacement}----如果变量var的后缀匹配pattern，那么就是用replacement来替换匹配到的pattern字符串
　　#! /bin/bash
　　v0=abc1234zip1234abc
　　echo "v0 = $v0"
　　echo
　　v1=${v0/#abc/ABCDEF}
　　echo "v1 = $v1"
　　v2=${v0/%abc/ABCDEF}
　　echo "v2 = $v2"
　　echo
　　v3=${v0/#123/100}
　　echo "v3 = $v3"
　　v4=${v0/%123/100}
　　echo "v4 = $v4"
　　exit 0