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This article will explain in detail what the meaning of the Linux $variable is, and the content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

Take. / xx.sh start 112113 as an example

$# number of parameters passed when executing the script ($# = 3)

Parameters passed by $@ ($@ = start 112113)

$0-script file itself ($0=./xx.sh)

$1-the first parameter passed to the script ($1=start)

$2-the first parameter passed to the script ($213112)

$3-the first parameter passed to the script ($313)

$- pid of the current process

Replace $() with "- command (command subsititution)

$()-Mathematical operations (arithmetical operation)

${}-used as a variable replacement (variable subsititution) also has some special functions, see attachment

History usage: see man 3 history

!!-Last order

! ^-the first argument of the last command

! $- the last argument of the previous command

! *-all parameters of the previous command

!:-the command itself

!: 3-specify the third parameter

!: 2-5-specify 2 to 5 parameters

!:-3-specify 0 to 3 parameters

!: 2 parameters-specify 2 to the last parameter

!: 2-- specify 2 to the last two parameters

!: s/xx/yy-replace xx with yy in the last command

Special functions of ${} are attached

${}-used to replace variables (variable subsititution)

${} operation on the array:

A = (abc def ghij) $An is defined array

${A [@]} and ${A [*]} get all the arrays

Example: for i in ${A [@]}; do echo $I; done

${A [2]} get the second group number of all arrays

${# A [@]} and ${# A [*]} get the number of arrays

${# A [2]} and ${# A [2]} get the length of the second array of the array, that is, the length of def

A [3] = okaywangbin assigns the third group number of the array

${} is a string operation

Suppose we define a variable as follows:

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

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

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

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

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

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

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

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

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

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

The method of memory is:

[list] # is to remove the left side (on the identification plate # to the left of $)

% is removed from the right (on the identification plate,% is to the right of $)

A single symbol is a minimum match; two symbols are a maximum match. [/ list]

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

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

We 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}: convert all dir to 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 processed)

${file:-my.file.txt}: if $file is not set or is null, 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 if it is not set)

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

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

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

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

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

About what the meaning of the Linux $variable is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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