Shulou(Shulou.com)06/02 Report--

Suppose we define a variable as follows:

File=/dir1/dir2/dir3/my.file.txt

You can replace it with ${} to get different values:

${file#*/}: delete the first / and the string to its left: dir1/dir2/dir3/my.file.txt

${file##*/}: delete the last / and the string to its left: my.file.txt

${file#*.}: delete the first one. And the string to its left: file.txt

${file##*.}: delete the last one. And the string to its left: txt

${file%/*}: delete the last / and the string to the right: / dir1/dir2/dir3

${file%%/*}: delete the first / and the string to its right: (null)

${file%.*}: delete the last one. And the string to the right: / dir1/dir2/dir3/my.file

${file%%.*}: delete the first one. And the string to the right: / dir1/dir2/dir3/my

The method of memory is:

# is to remove the left (on the keyboard # to the left of $)

% is removed from the right side (% on the keyboard is on the right side of $)

A single symbol is a minimum match; two symbols are a maximum match.

${file:0:5}: extract the leftmost 5 bytes: / dir1

${file:5:5}: extract 5 consecutive bytes to the right of the fifth byte: / dir2

You can also replace the string in the value of the variable:

${file/dir/path}: replace the first dir with path:/path2/dir2/dir3/my.file.txt

${file//dir/path}: replace all dir with path:/path2/path3/path4/my.file.txt

Using ${}, you can also assign values for different variable states (no settings, null values, non-null values):

${file-my.file.txt}: if $file is not set, my.file.txt is used as the return value. (null and non-null values are not dealt with)

${file:-my.file.txt}: if $file is not configured or is a null value, my.file.txt is used as the return value. (not processed when non-null)

${file+my.file.txt}: if $file is set to null or non-null, my.file.txt is used as the return value. (no processing at setting time)

${file:+my.file.txt}: if $file is a non-null value, my.file.txt is used as the return value. (no processing when no settings and null values)

${file=my.file.txt}: if $file is not set, use my.file.txt as the return value and set $file to my.file.txt at the same time. (null and non-null values are not dealt with)

${file:=my.file.txt}: if $file is not set or is null, use my.file.txt as the return value and set $file to my.file.txt at the same time. (not processed when non-null)

${file?my.file.txt}: if $file is not configured, input my.file.txt to STDERR. (null and non-null values are not dealt with)

${file:?my.file.txt}: if $file is not set or is null, output my.file.txt to STDERR. (not processed when non-null)

${# var} calculates the length of the variable value:

${# file} gets 27 because / dir1/dir2/dir3/my.file.txt is 27 bytes

Transferred from: http://space.baidu.com.cn/ugo5/blog/item/c550bbc54d1644079c163dbd.html

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.