How to check if a string is in an array? How to use the Bash ternary operator? How to negate an if condition in a Bash if statement? (if not command or if not equal) How to use the BASH_REMATCH variable with the Regular Expression Operator =~?
if ! getent passwd "$username" >/dev/null; then echo "User $username does not exist" fi The!operator in front of the getent command is used to negate the exit code and theifstatement then checks the negated exit code.
/bin/bashif[`whoami`!='root'];then echo"Executing the installer script"./home/oracle/databases/runInstaller.shelseecho"Root is not allowed to execute the installer script"fi Executing the scriptasa root user,#./preinstaller.sh Root is not allowed to execute the installer script 在此示例中,...
Conclusion Theif,if...elseandif...elif...elsestatements allow you to control the flow of the Bash script’s execution by evaluating given conditions. If the condition evaluated to false, the code in the optionalelseclause will be executed. ...
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command ...
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the fol‐ ...
command || true Don't skimp on if-statements. You can't use && as a shorthand if-statement without always using || as an else-branch. Otherwise, the script terminates if the condition is false.Bad:command && … Good (contrived):command && … || true ...
We use the Bash built-in test mechanism to check if the length of $1 is nonzero. If the length of $1 is zero, then clearly nothing was entered. In that case, our if/then statement echoes that there was an error, shows the proper usage of the script, then exits. Note the $0 ...
For example, you can easily create the3x10.shscript with an until loop instead of a while loop; the trick here is to negate the test condition: #!/bin/bash num=1 until [ $num -gt 10 ]; do echo $(($num * 3)) num=$(($num+1)) done ...
bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. An attempt is first made to open the file in the current directory, and if no file is found, the shell searches the directories in PATH for the ...