Question: What Is $? In Shell Scripting?

What does $$ mean in bash?

$$ is the pid (process id) of the shell interpreter running your script.

It’s the process ID of the bash process..

How do I know if I have bash or zsh?

To test the above, say bash is the default shell, try echo $SHELL , and then in the same terminal, get into some other shell (KornShell (ksh) for example) and try $SHELL . You will see the result as bash in both cases. To get the name of the current shell, Use cat /proc/$$/cmdline .

What is difference between Perl and shell scripting?

Shell scripts can run on any computer with a shell interpreter. … Basically shell scripts have more portability as most computers have a bash shell built-in. Perl has to be installed, isn’t built-in in all systems. Perl api is easier more readable and Perl is faster than shell scripts in most general projects.

What is $1 in shell scripting?

$1 is the first command-line argument passed to the shell script. … $0 is the name of the script itself ( $1 is the first argument (filename1) $2 is the second argument (dir1)

What is shell scripting with examples?

A shell script is a list of commands in a computer program that is run by the Unix shell which is a command line interpreter. A shell script usually has comments that describe the steps. The different operations performed by shell scripts are program execution, file manipulation and text printing.

How do you find out what’s your shell?

How to check which shell am I using: Use the following Linux or Unix commands: ps -p $$ – Display your current shell name reliably. echo “$SHELL” – Print the shell for the current user but not necessarily the shell that is running at the movement.

What is difference between Bash and Shell?

Bash stands for “Bourne Again SHell”,and is a replacement/improvement of the original Bourne shell (sh). Shell scripting is scripting in any shell, whereas Bash scripting is scripting specifically for Bash.

What is $$ in Linux?

$$ is the process ID (PID) of the script itself. $BASHPID is the process ID of the current instance of Bash. This is not the same as the $$ variable, but it often gives the same result.

What does $? Mean in shell script?

$? -The exit status of the last command executed. $0 -The filename of the current script. $# -The number of arguments supplied to a script. $$ -The process number of the current shell. For shell scripts, this is the process ID under which they are executing.

Why shell scripting is used?

Using a shell script is most useful for repetitive tasks that may be time consuming to execute by typing one line at a time. A few examples of applications shell scripts can be used for include: Automating the code compiling process. Running a program or creating a program environment.

What is $0 shell?

Definition: A child process is a subprocess launched by another process, its parent. Positional parameters. Arguments passed to the script from the command line [1] : $0, $1, $2, $3 . . . $0 is the name of the script itself, $1 is the first argument, $2 the second, $3 the third, and so forth.

What is bash used for?

Bash is a command processor that typically runs in a text window where the user types commands that cause actions. Bash can also read and execute commands from a file, called a shell script.

What is the use of $# in shell scripting?

$# Stores the number of command-line arguments that were passed to the shell program. $? Stores the exit value of the last command that was executed. $0 Stores the first word of the entered command (the name of the shell program).

How do I know if Im using bash or zsh?

Check the SHELL environment variable. If it contains fish , zsh , bash , ksh or tcsh , the user’s favorite shell is probably that shell.

How do I specify which Shell is used when I login?

chsh command syntax -s {shell-name} : Specify your login shell name. You can obtained list of avialble shell from /etc/shells file. User-name : It is optional, useful if you are a root user.