The exit status of a command

From Linux Shell Scripting Tutorial - A Beginner's handbook
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Each Linux command returns a status when it terminates normally or abnormally. You can use command exit status in the shell script to display an error message or take some sort of action. For example, if tar command is unsuccessful, it returns a code which tells the shell script to send an e-mail to sys admin.

  • Every Linux command executed by the shell script or user has an exit status.
  • The exit status is an integer number.
  • The Linux man pages stats the exit statuses of each command.
  • 0 exit status means the command was successful without any errors.
  • A non-zero (1-255 values) exit status means command was failure.
  • You can use special shell variable called ? to get previously executed command. To print ? variable use the echo command (echo $?