变量替换操作
-
${VAR:-value} 如果变量为空，返回新值。
-
${VAR:=value} 如果变量为空，返回新值且付给变量。
-
${VAR:?message} 如果变量为空，显式一条消息。
-
${VAR:offset:length} 截取变量的一部分。
模式匹配操作
-
${VAR#pattern} 匹配第一个，返回后面的。
-
${VAR##pattern} 匹配最后一个，返回后面的。
-
${VAR%pattern} 从后向前匹配第一个，返回前面的。
-
${VAR%%pattern} 从后向前匹配至最前，返回前面的。
#!/bin/bash
PASSWD_PATH=$(which passwd)
echo "\$PASSWD_PATH is $PASSWD_PATH"
echo "\${PASSWD_PATH#*/} is ${PASSWD_PATH#*/}"
echo "\${PASSWD_PATH##*/} is ${PASSWD_PATH##*/}"
echo "\${PASSWD_PATH%/*} is ${PASSWD_PATH%/*}"
echo "\${PASSWD_PATH%%/*} is ${PASSWD_PATH%%/*}"
正则表达式
-
^text - Line starts with text
-
text$ - Line ends with text
-
. - Wildcard, match any single character
-
[abc], [a-c] - Matchs a, b or c.
-
* - Matches 0 or an infinitive number of the previous character.
-
\{2\} - match exactly 2 of the previous character.
-
\{1, 3\} - minimum 1 and maximum 3 of the previous character.
-
colou?r - color or colour
数值计算
- $((1 + 1))
- let X="$1 $2 $3"; echo $X
- echo "scale=9; 10/3" | bc
