bg - macOS

Overview

The bg command in macOS resumes suspended jobs in the background, allowing them to continue running without occupying the terminal directly. Primarily used in multi-tasking environments, it is instrumental when you need to continue working in the terminal without interruption from ongoing processes.

Syntax

The basic syntax of the bg command is:

bg [job_spec]
  • [job_spec]: Optional parameter that specifies the job to put in the background. If no job_spec is provided, the most recent job is used.

Options/Flags

The bg command doesn’t typically have options or flags. Its functionality is straightforward, focusing on resuming suspended jobs in the background.

Examples

  1. Resuming the Most Recent Job:
    If you’ve just suspended a job by pressing Ctrl + Z, you can resume it in the background simply by typing:

    bg

  2. Resuming a Specific Job:
    If multiple jobs are suspended, you can list them with the jobs command and then resume a specific one using its job number:

    jobs
bg %1

    Here, %1 refers to the job number which is typically shown at the beginning of the line when using the jobs command.

Common Issues

  • No Current Job:
    If there are no recently suspended jobs, the bg command will return an error. Always ensure a job is suspended before using bg.

  • Job Spec Error:
    If an incorrect job spec is given, such as a non-existent job number, the bg command will also return an error. Double-check job numbers by using the jobs command.

Integration

The bg command integrates well with job control and other shell features. A common use case involves combining bg with jobs, fg for foregrounding jobs, and kill for terminating jobs:

# Suspend the current job
Ctrl + Z
# List all jobs
jobs
# Resume job number 1 in the background
bg %1
# Eventually bring the job back to foreground if needed
fg %1
  • fg: Brings jobs to the foreground, allowing for interactive continuation.
  • jobs: Lists the current jobs along with their statuses.
  • kill: Sends a signal to a job, commonly used to terminate a job.

You can find more details in the official Bash documentation or the macOS terminal manual pages accessible via the man command, such as man bash for shell built-ins or man kill for signal-related commands.