printf "Enter a number between 10 and 20 inclusive: " read number if (( number < 10 )) then printf "%d is too low\n" "$number" >&2 exit 1 elif (( number > 20 )) then printf "%d is too high\n" "$number" >&2 exit 1 else printf "You entered %d\n" "$number" fi 注...
Here you try to regularly kill (TERM signal) the process nicely after 10.0 seconds after it has started. If it's still running after 20.0 seconds, then send a KILL signal (kill -9). If in doubt, check which signals are supported in your system (kill -l, for example). If this isn'...
You may need to perform the function testing several times. The first time you run it, you will likely find some errors in your scripts or in the procedures. Therefore, to avoid wasting too much time in recreating the server environment from scratch -- especially if a database is involved ...
If you’re making Bash programs for you or for others to use one way you can get user input is to specify arguments for users to provide to your program, as we discussed in the previous section. You could also ask users to type in a string on the command line by temporarily stopping ...
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 ...
It will execute the first command then stop if successful, if not, it will proceed pass failed commands until one is successful and stop. && The AND operator is used to chain commands. It will execute commands only if the first command is successful and proceed until one fails. ; 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 following command ...
Checking the Exit Status of a Command Every command in Bash returns anexit status: 0means the command was successful. Any number other than0means something went wrong. We can use this exit status to handle errors. For example, let’s check if a file exists before trying to copy it: ...
\!: the history number of this command \#: the command number of this command \$: if the effective UID is 0, a #, otherwise a $ \j: the number of jobs currently managed by the shell Adding Colors to the Prompt Mostly, system admins would like to add some color to their dull sh...
If you run a command and then realize it will take longer to complete than you thought, you can pause it using Ctrl-Z, which will return you to a prompt. You can then typebgto unpause the job and continue running it in the background.This is basically adding a trailing&after the fac...