操作字串

ref: http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/string-manipulation.html

就直接 copy ...

Substring Removal

${string#substring}
Strips shortest match of $substring from front of $string.

${string##substring}
Strips longest match of $substring from front of $string.

stringZ=abcABC123ABCabc
#       |----|
#       |----------|

echo ${stringZ#a*C}      # 123ABCabc
# Strip out shortest match between 'a' and 'C'.

echo ${stringZ##a*C}     # abc
# Strip out longest match between 'a' and 'C'.

反過來：

${string%%substring}
Strips longest match of $substring from back of $string.

stringZ=abcABC123ABCabc
#                    ||
#        |------------|

echo ${stringZ%b*c}      # abcABC123ABCa
# Strip out shortest match between 'b' and 'c', from back of $stringZ.

echo ${stringZ%%b*c}     # a
# Strip out longest match between 'b' and 'c', from back of $stringZ.

return value from shell script

ref: http://tldp.org/LDP/abs/html/exit-status.html

是用 exit 指令。

exit 123

然後 caller 用 $? 就可以取得上一個 script exit 的值。

example : disk usage 超過90% , 刪除Android folder

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ref: http://stackoverflow.com/questions/19703621/get-free-disk-space-with-df-to-just-display-free-space-in-kb