execline: the foreground command
Keywords: execline command foreground

execline
Software
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# The `foreground` program

`foreground` executes a sequence of commands.

## Interface

In an execlineb script:

         foreground { prog1... } prog2...

- `foreground` reads prog1 in a block. It forks and executes it, then waits for it to complete.
- `foreground` sets the `?` environment variable to the exit code of prog1. If prog1... was killed by a signal, the `?` value is 256 plus the signal number.
- `foreground` then execs into prog2....

## Notes

- `foreground` is the basic sequence operator: it takes two commands and executes them one by one. execline scripts require it to wrap external commands that exit instead of natively supporting the "perform some action, then execute some other program" model.
- `foreground prog1... "" prog2...` is equivalent to `sh -c 'prog1... ; exec prog2...'`.
- 256 and above are not valid exit codes for commands, so when the `?` environment variable contains 256 or more, it means that the previous command was killed by a signal. There is no ambiguity here, and `?` reports exactly what happened to the previous command; `foreground` does not exit, so there is no need for exit code approximation.