Tuesday, June 3, 2008

Shell scripting built-in variables

When doing scripting in shell, like bash, there are a few built-in variables that we can use to optimize our script. Below are a few useful ones:

  • $$ = The PID number of the process executing the shell.
  • $? = Exit status variable.
  • $0 = The name of the command you used to call a program.
  • $1 = The first argument on the command line.
  • $2 = The second argument on the command line.
  • $n = The nth argument on the command line. n = 0-9
  • $* = All the arguments on the command line.
  • $# = The number of command line arguments.
Hope this can help

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