Linux Shell学习（7）
1. 检查变量是否存在，如果不存在，则赋予默认值。
var=${NAME-default}
e.g.
#!/bin/bash
argu=${*-noargu}
editor=${EDITOR-emacs}
echo $editor
echo $argu
等价于
#!/bin/bash
#argu=${*-noargu}
[ -z "$*" ] && argu=noargu || argu=$*
#editor=${EDITOR-emacs}
[ -z $EDITOR ] && editor=noeditor || editor=$EDITOR
echo $editor
echo $argu
root@localhost :/home/James/mypro/shell/TryOut# ./test.sh
noeditor
noargu
root@localhost :/home/James/mypro/shell/TryOut# ./test.sh hello
noeditor
hello
root@localhost :/home/James/mypro/shell/TryOut# ./test.sh hello nice to meet you
noeditor
hello nice to meet you
2. 如何获得某个文件中的内容
var=$(<filename)
var=$(cat filename)
3. memu box
menu box和input box有点类似，也是用标准错误输出来导出用户的输入选择。
e.g.
#!/bin/bash
MAIL="<[email protected]>"
# store menu options selected by the user
INPUT=/tmp/menu.sh.$$
# Storage file for displaying 'date' and 'cal' command's output
OUTPUT=/tmp/output.sh.$$
# trap and delete tmp files
trap 'rm ${INPUT}; rm ${OUTPUT}; exit' SIGHUP SIGINT SIGTERM
#
# Purpose - display output using msgbox
# $1 -> set msgbox height
# $2 -> set msgbox width
# $3 -> set msgbox title
#
display_output() {
local h=${1-10}
local w=${2-40}
local t=${3-Output}
dialog --backtitle "$MAIL" \
--title "${t}" \
--clear \
--msgbox "$(<$OUTPUT)" ${h} ${w}
}
#
# Purpose - display current system's date and time
#
show_date() {
echo "Today is $(date) @ $(hostname -f)." > $OUTPUT
display_output 10 40 "Date and Time"
}
#
# Purpose - display a canlendar
#
show_cal() {
cal > $OUTPUT
display_output 20 40 "Calendar"
}
#
# set infinite loop
#
while true; do
### display main menu ###
dialog --clear --help-button --backtitle "$MAIL" \
--title "[ M A I N - M E N U ]" \
--menu "You can use the UP/DOWN array keys, the first \n
letter of the choice as a hot key, or the \n\
number keys 1-9 to choose an option.\n\
Choose the TASK" 15 50 4 \
Date/Time "Display date and time" \
Calendar "Display a calendar" \
Exit "Exit to Shell" 2>$"${INPUT}"
menuitem=$(<"${INPUT}")
# make decisions
case $menuitem in
Date/Time) show_date;;
Calendar) show_cal;;
Exit) echo "Bye"; break;;
*) echo "NOT RECOGNIZED: ${menuitem}"; break;;
esac
done
# rm temp file if any
[ -f ${INPUT} ] && rm ${INPUT}
[ -f ${OUTPUT} ] && rm ${OUTPUT}
4. seq命令
for ((i=begin;i<=end;i=i+step)
<==>
for i in $(seq begin step end)
5. A progress bar
echo percentage | dialog --gauge "text" height width percent
echo "10" | dialog --gauge "Please wait" 10 70 0
echo "50" | dialog --gauge "Please wait" 10 70 0
echo "100" | dialog --gauge "Please wait" 10 70 0
将某个命令的输出，重定向到gauge box的输入来控制gaugebox。
dialog --title "Copy file" --gauge "Copying file ..." 10 70 << (
command 1
command 2
...
command N
)
6. Shell中的array类型的操作，设置和读取
2031 array=(/bin/* /etc/*)
2032 cat ${#array[*]}
2033 echo ${#array[*]}
2034 for f in ${array[@]}; do echo $f; done
2035 echo ${array[1]}
2036 echo ${array[0]}
2037 echo ${array[100]}
2038 echo ${array[*]}
2039 echo ${array[@]}
7. console management
tput command
root@localhost :/home/James/mypro/algorithm# tput cols
168
root@localhost :/home/James/mypro/algorithm# tput lines
47
root@localhost :/home/James/mypro/algorithm# tput cup $(($(tput lines)/2)) $(($(tput cols)/2)); echo 'Hello World!'
Hello World!
root@localhost :/home/James/mypro/algorithm#