To Bash or not to Bash

Writing shell scripts can automate command execution and help us become more productive. Bash is the default shell for most linux distributions.

Which Bash

Check that your have Bash installed.

$ which bash
/usr/bin/bash

Bash process

To check which shell that you are currently using, we can use ps to report the current shell process.

$ ps -p $$
PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
143      88     143      12484  pty0      197609 21:39:51 /usr/bin/bash

$SHELL variable

Alternatively, you can echo the $SHELL variable which specifies your user default shell. It is only true if you have not switched your shell since login.

$ echo "$SHELL"
/usr/bin/bash

Security

Do not run any scripts from untrusted sources! Always avoid running scripts with root or sudo unless you know what it does.

Basic bash script structure

Usually a shell script has the file extension .sh, but it can be anything. It is just a text file that is up to the shell to interpret the contents.

hello.sh

#!/bin/bash

echo "Hello World"
echo 'I am also a string'

A bash script should always start with #!/bin/bash. Although the script will run just fine without it, it is a convention that indentifies itself as a bash script.

Assuming the shell script above is store in a file named hello.sh, to execute the bash script:

$ ./hello.sh
Hello World
I am also a string

Remember to add execution permission to the script.
For example: chmod +x hello.sh

Writing Bash Scripts