If you want to achieve the else part execution in the shell terminal, you must have to delete the directory so that the condition doesn’t get satisfied. Therefore, we have deleted the newly made empty directory “new” from the home folder of our Ubuntu 20.04 system. After this, we have...
By setting a size threshold, you can customize the script to check if the file is empty based on your specific needs. Since the file I am checking is empty, the bash script will show that the file is empty and one thing to remember is that I have set the threshold to 1 Byte because...
In this example, the substitution command is used with $() to capture the output of grep, and then the -z option of the test command is used to check if the resulting string is empty or not. Here, the grep command searches for the pattern pattern in the file dummy.txt. The output...
进入命令行环境以后,一般就已经打开Bash 了。如果你的 Shell 不是 Bash,可以输入bash命令启动Bash。 $ bash 退出Bash 环境,可以使用exit命令,也可以同时按下Ctrl + d。 $ exit Bash 的基本用法就是在命令行输入各种命令,非常直观。作为练习,可以试着输入pwd命令。按下回车键,就会显示当前所在的目录。 $ pwd /...
#文件测试操作-d FILE_NAM # TrueifFILE_NAM is a directory-e FILE_NAM # TrueifFILE_NAM exists-f FILE_NAM # TrueifFILE_NAM existsandis a regular file-r FILE_NAM # TrueifFILE_NAM is readable-s FILE_NAM # TrueifFILE_NAM existsandisnotempty...
Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "String is not empty" fi For more Shell scripting tips,check out or Bash/Shell scripting articles!
Checking If Variable Is Empty in Bash There are multiple ways to check if a variable is empty or not. Before moving towards those methods, knowing when a variable is called empty is necessary. In Bash, a variable is called empty if: A variable is declared without assigning any value to ...
mkdir:Make Directory(创建目录) touch:touch man:Manual su:Swith user(切换用户) cd:Change directory ls:List files mkfs:Make file system fsck:File system check uname:Unix name lsmod:List modules mv:Move file cp:Copy file ln:Link files
How to check if a variable exists or is “null”? How to check if a file exists? How to check if a directory exists? How to check if a command succeeds or failed? How to do string comparison and check if a string equals to a value? How to check if a string is in an array?
1: > data.xxx # File "data.xxx" now empty.等价于 cat /dev/null >data.xxx如果以追加方式的重定向，则对文件不构成任何修改。同样如果文件不存在也会新建一个。例如 : >> data.xxx 。注意 这个只能在普通文件中使用，不能在管道，符号链接和其他特殊文件中使用；你也可以作为域分隔符，比如环境变量$...