How do you run shell commands as foreground and background processes? Give an example for each.

To run a shell command as a foreground process, simply type the command in the terminal and hit enter. The command will run in the foreground and the terminal will be blocked until the command completes. For example:

$ ls -l

To run a shell command as a background process, add an ampersand (&) at the end of the command. This will allow you to continue using the terminal while the command runs in the background. For example:

$ sleep 10 &

This command will run the "sleep 10" command in the background, and return control of the terminal to you immediately. The sleep command will run for 10 seconds in the background before completing.

相关问题

do me a example for shell command exec usage

Sure, here's an example of using the shell command `exec` in a shell script:

#!/bin/bash

# Execute a command and redirect its output to a file
exec ls -l > /tmp/list.txt

# The following command will not be executed
echo "This will not be printed to the console"

In this example, the `exec` command is used to run the `ls -l` command and redirect its output to a file named `/tmp/list.txt`. After the `exec` command completes, the script will continue to execute any remaining commands in the script. However, in this case, the `echo` command will not be executed because the `exec` command replaces the current shell process with the `ls` command.

28. You are starting a new year and need to create ten empty files for your accounting system. Which of the commands or operators enable you to quickly create these files?

To quickly create ten empty files, you can use the touch command with curly braces and a sequence expression. For example:

touch file_{1..10}.txt

This will create ten files with names "file_1.txt", "file_2.txt", and so on, up to "file_10.txt". The touch command updates the last modified date of the file, so by creating an empty file with touch, you are essentially creating a new file.

Another option is to use a for loop in the bash shell. For example:

for i in {1..10}; do touch file_$i.txt; done

This will create the same ten files as the previous example. The for loop iterates over the sequence of numbers from 1 to 10, and for each iteration, it runs the touch command to create a new file with a unique name.