Useful tips for the bash shell.

There are many useful tricks for the bash shell. This is how to show a count of all running jobs in the terminal.

Here are two ways to display the current number of jobs in your bash shell prompt:

1. Using the \j escape sequence:

PS1='\u@\h:\w \j\$ '

The /j escape sequence will show the jobs count.

Here’s what each part does:

• \u: Username
• @\h: Hostname
• :\w: Current working directory
• \j: Number of background jobs
• \$: Prompt symbol (usually $)

2. Conditional display with PROMPT_COMMAND:

This method allows you to only show the job count if any jobs are running. Add the following lines to your ~/.bashrc file:

PROMPT_COMMAND='hasjobs=$(jobs -p)'
PS1='${hasjobs:+\j }\$ '

Here, the PROMPT_COMMAND variable runs the jobs -p command before displaying the prompt. If any jobs are found, the hasjobs variable will be non-empty, and the \j escape sequence will be displayed.

You have several options to show different prompts based on an SSH connection:

1. Using $SSH_TTY variable:

• This checks if a terminal is allocated for the session. It’s typically set for interactive SSH sessions but not for script execution via SSH.
• Add the following lines to your ~/.bashrc file:

if [[ -n "$SSH_TTY" ]]; then
  PS1='SSH:\u@\h:\w\$ '
else
  PS1='\u@\h:\w\$ '
fi

• This sets a different prompt with “SSH:” prefix when connected via SSH and a regular prompt otherwise.

2. Checking $TERM variable:

• This variable holds the terminal type being used. Specific values like “dumb” or “xterm” might indicate non-interactive sessions.
• Add the following lines to your ~/.bashrc file:

if [[ "$TERM" =~ ^(dumb|xterm)$ ]]; then
  PS1='\u@\h:\w\$ '
else
  PS1='SSH:\u@\h:\w\$ '
fi

• This sets the SSH prompt only if the terminal type suggests a non-interactive session.

3. Using ps1_ssh() function:

• This method allows more complex logic and customization.
• Add the following code to your ~/.bashrc file:

ps1_ssh() {
  if [[ -n "$SSH_TTY" ]]; then
    echo "SSH: \u@\h:\w"
  else
    echo "\u@\h:\w"
  fi
}
 
# Set the prompt function
PS1="$(ps1_ssh)$ "

• This defines a function ps1_ssh that checks for SSH connection and returns the desired prompt. Then, it sets the PS1 variable to the output of this function.

4. Using shell configuration files on remote servers:

• If you want to customize the prompt on remote servers where you connect via SSH, you can edit the configuration files like .bashrc or .zshrc on those servers.
• This allows you to set different prompts specifically for users connecting via SSH.