Shell

$ () and ' (anti-quote)In the bash shell, $ () and "(anti-quote) are used for command substitution.The so-called command substitution is similar to the variable substitution we learned in the fifth chapter, which is used to reorganize the command

First, the basic use of EvalEval will scan the back of the CmdLine two times, if after the first scan, cmdline is a normal command, then execute this command;If the cmdline contains an indirect reference to a variable, the semantics of the indirect

Thank you for the 36,000 sectionCommon Shell Categories: BASH: is the GNU Bourne Again Shell, which is the default shell on the GNU operating system C Shell: The BSD version of Sun's shell Look at where the shell is on the

Yesterday, the Dragon Boat Festival, the evening when a phone call, my friend's company, the database was two work not long phper to break, the specific is to put a field value, to the whole table into a name, of course, this is can be configured to

1. What role does Eval have in the shell? Could you give me an example?Role:#!/bin/bashAa=h1Bb=h2var= (AA bb)For VAS in ${var[@]}Do Echo $vas Eval Var_temp=\$${vas} Echo $var _tempDone2. What is the role of dirname? Could you give me an

First, the user logged into the system after the system environment variables:$HOME user's own directory$PATH the directory that was searched when the command was executed$TZ Time Zone$MAILCHECK How many seconds to check if there are new letters$PS 1

#case: ESAC statement: with switch. Case similar, is a multi-branch selection structure#case语句匹配一个值或一个模式 if the match succeeds in executing the corresponding command, if the match does not execute the * command successfully#;; Similar to break, the

The following is an explanation under the bash environment.One, single parenthesis ()Two, double parenthesis (())Can be used as a numerical condition or as a numerical operation (approximate to let command)Like the C language syntax, supports

Wildcard charactersWildcard characters can be used in place of a character. Typically, the asterisk "*" matches 0 or more characters, a question mark "?" Matches a 1 character.Use case:1. Files and directoriesWhen describing file names (or paths) in

While loop: Tests a condition repeatedly, as long as the condition is set up and executed repeatedlyThe condition can be: test the expression, or the Boolean value true (the condition is always true) and false (the condition is always false)vi

For i in a B CDoEcho $iDone!ser Historical complements> Correct information output file>> correct information output file, append2> error message output file2>> error message output file append&>> all outputsfree-m | Grep-i Mem | awk ' {print $4,$3}

Z Shell ' s (zsh) popularity has increased in the last years. I have no moved too zsh yet, but I am going to do.Zsh is isn't installed in Linux by default, but it can be installed easilly with a package Manager:1. Check If ZSH is already installed

Shell-0. Introduction1. Use shell scripts in those environments• Application environment: Several complex parameters are required to execute certain commandsRequires multiple commands for State view and maintenance management of the systemRegular

First, define variablesWhen defining a variable, the variable name does not have a dollar sign ($), such as:Variablename= "Value"Note that there can be no spaces between the variable name and the equals sign, which may be different from any

Sometimes we use a function often, it is very troublesome to assign a value in each script, this time we can write the function that we use frequently in the form of function library.A very simple little example: do we need to know which version of

First, file comparison operators-e filename true if filename exists [-e/var/log/syslog]-D filename True if filename is a directory [-d/tmp/mydir]-F filename True if filename is a regular file [-f/usr/bin/grep]-L filename True if filename is a

I. Digital testingFormat: N1-op n2Test Operation op:EQ/NE/LE/GE/LT/GT--equals/not equals/less than equals/greater than/less than/greater than1. A numeric comparison can use a special (()) operator, which is closer to the C language, see digital

Using the remote shell tool SSH login to the Linux host, the user name after the return to the card, 10 seconds after the prompt to enter the password.Use Wireshark to catch the whole process packageBecause SSH is an encrypted protocol, it is not

Sed is a stream editor, which is a very useful tool in text processing and can be used perfectly in conjunction with regular expressions. When processing, the currently processed rows are stored in a temporary buffer called pattern space, followed

Original: https://leetcode.com/problems/word-frequency/Write a bash script to calculate the frequency of each wordinchA textfilewords.txt.For simplicity sake, you could assume:words.txt contains only lowercase characters and space' 'characters. Each