# checkingifa directory existsif[ -e $HOME ]thenecho"OK on the directory, now let's check the file"# checkingifafileexistsif[ -e $HOME/testing ]then# thefileexists, append data to itecho"Appending date to exist
Here I will show you how to check if a Linux user exists (or does not exist) in a POSIX-compatible shell like Bash or Dash. I will use thegetentcommand along with the/etc/passwdfile for this. Example Bash script: if getent passwd "$username" >/dev/null; then echo "User $username ...
Next, let’s check out if user peter exists in the /etc/passwd file using the getent command: $ getent passwd peter peter:x:1000:1000:PETER KARANJA,,,:/home/peter:/bin/bashCopy This command allows us to read various text files known as databases. It has various options for databases,...
In Bash, you can use the test command to check whether a file exists and determine the type of the file.The test command takes one of the following syntax forms: test EXPRESSION [ EXPRESSION ] [[ EXPRESSION ]] Copy If you want your script to be portable, you should prefer using the ...
if TEST-COMMANDS; then CONSEQUENT-COMMANDS; fi TEST-COMMAND执行后且它的返回状态是0,那么CONSEQUENT-COMMANDS就执行。返回状态是最后一个命令的退出状态,或者当没有条件是真的话为0。 TEST-COMMAND经常包括数字和字符串的比较测试,但是也可以是任何在成功时返回状态0或者失败时返回一些其他状态的一些命令。一元表达式...
When making a symbolic link, check the command twice before you run it because several things can go wrong. For example, if you reverse the order of the arguments (ln -s linkname target), you’re in for some fun if linkname is a directory that already exists. If this is the case (...
syntastic_check_on_open = 1 " let g:syntastic_check_on_wq = 0 " let g:syntastic_cpp_checkers = ['gcc'] " let g:syntastic_cpp_compiler = 'g++' " let g:syntastic_cpp_compiler_options = '-std=c++11 -stdlib=libc++' " "if !exists('g:syntastic_cpp_compiler_options') " " let...
command:要执行的程序路径(设置为绝对路径) 2.crontab命令的使用方法 格式: crontab [选项] 选项: e:编辑一个新的计划任务 l:显示计划任务 r:删除计划任务 实例: # crontab -e //创建计划任务 00 * * * * root /usr/bin/date # crontab -l //查看计划任务 00 * * * * root /usr/bin/date # ...
echo "This is my second command" echo "I can even put in other commands besides echo:" ls -a /home/$testuser/.b* fi 用户里没有Christine,所以没有打印。使用if-then-else。 2.if-then-else语句 在if-then语句中,不管命令是否成功执行,你都只有一种选择。如果命令返回一个非零退出状态码,bash ...
# Check if a file exists if [ -f $file ] then echo "File exists" else echo "File does not exist" fi # Check if a command is successful if ls then echo "Command succeeded" else echo "Command failed" fi ``` 通过使用if-else语句,用户可以根据不同的条件执行不同的操作。这使得Bash脚本...