Inside the shell the meaning of the beginning of the $, as well as the extension

For the set in the shell and the use of eval:

Set position parameters (same as command line script)

The role of Eval is to describe the second time

[Email protected]:/home/xpg# set--Hello Shanghai Liangge [email protected]:/home/xpg# eval echo \$$ #liangge [email PR otected]:/home/xpg#

The role of "$" inside the shell:

$: script Name

If you want to get the path to the script and the name of the script, you can use DirName and basename

[Email protected]:/home/xpg# dirname/home/xpg/1.sh/home/xpg[email protected]:/home/xpg# basename/home/xpg/1.sh 1.sh

$n: Output Specific parameters

$#: Total number of parameters

$*: And the following [email protected] is the same without the quotation marks

[Email protected]: The difference with the quotation marks. You can use set to set the position parameters to see, these two generally do not

$?: The judgment of the previous command, if correct, is 0, otherwise nonzero

Usage of $ in enterprise:

Determine script command, whether the script executes successfully

* If in the script, use Exit N to return the number to $?

* If you use return in the function, return the number to $?

$$: Get the script's process number

The example of production is the execution of a script multiple times, the first time did not finish, the second is to first remove the PID of the script, in the use of $$ to determine the PID of the script

Built-in commands for bash shell:

Echo

-N: Do not wrap output content

-E: Parsing the escape character (used below)

\ n: Line break

\ r: Enter

\t:tab Jian

\b: Backspace

[Email protected]:/home/xpg# echo me;echo youmeyou[email protected]:/home/xpg# echo-n me;echo youmeyou[email protected]  :/home/xpg# printf "log\tlog\npog\tpog\n" log logpog pog[email protected]:/home/xpg# echo-e "Log\tlog\npog\tpog" Log logpog pog[email protected]:/home/xpg# echo-e log\tlog\npog\tpog Logtlognpogtpog

EXEC: Executing the command will exit the current shell.

[Email protected]:/home/xpg# exec datemon Jan 07:07:25 PST 2018[email protected]:~ about shell variable quantum string knowledge and practice ${variable name}: Value ${#变量名} : Length ${variable name: num}: From num to the end, Num is a number ${variable name: num:num1}: Character ${variable name from num to NUM1 #word}: Remove the shortest matching word substring ${variable name from the beginning of the variable # #word} : delete longest matching word substring ${variable name from the beginning of the variable%word}: percent of percent removed from the right: delete the matching longest match from the right of the variable Word,word can be (A*c represents yes A to c,[0-9]) ${parameter/pattern/ String}: Use the first instead of the first matching pattern${parameter//pattern/string}: Use string instead of all pattern to modify the file name: Anaconda-ks.cfg stu_102_1_ Finished.jpg[[email protected] ~]# rename "_finished" "" *.jpg[[email protected] ~]# lsanaconda-ks.cfg stu_102_1.jpg

Inside the shell the meaning of the beginning of the $, as well as the extension