The execlineb program

execlineb reads and executes a script.
It is a command launcher: it reads a file, turns that file into a command line, then executes into that command line.


     execlineb [ -q | -w | -W ] [ -p | -P | -S nmin | -s nmin ] [ -e ] -c script [ args... ]


     execlineb [ -q | -w | -W ] [ -p | -P | -S nmin | -s nmin ] [ -e ] scriptfile [ args... ]

or in an executable file:

#!/command/execlineb [ -qwWpPSnmin ]

Parsing phase.

Environment management phase.

Execution phase.


See below for the other options.

Syntax of scripts

An execlineb script is a string that must not contain the null character. execlineb parses it and divides it into words. The parser recognizes the following components:

You can see an example of distinct execlineb components here.

In addition to that simple lexing, execlineb performs the following higher-level parsing:

For proper execution, the sequence of words must follow the execline grammar.

Options for block syntax checking

External execline commands that read blocks, like foreground, use the EXECLINE_STRICT environment variable: if it is set to 1, they will print a warning message on stderr if they find their blocks not to be properly quoted. If it is set to 2, they will also die. If it is set to 0, or unset, they won't complain at all.

Normally the EXECLINE_STRICT environment variable is inherited from the caller. You can force it unset, set to 1, or set to 2 by giving respectively the -q, -w or -W option to execlineb.

The EXECLINE_STRICT variable (as well as the -q, -w and -W options to execlineb) will also modify the behaviour of the -S nmin and -s nmin options when execlineb is called with less than nmin positional parameters:

Options for environment management

Normally, execline scripts are reentrant: environment variables potentially overwritten by execlineb, such as # or 0, are pushed. This is the standard, safe behaviour. Nevertheless, it is rather costly, and may be unneeded for small scripts: for those cases, execline comes with two options that bypass the environment management. Be warned that the purpose of these options is optimization, and you should not use them if you're not familiar with the way execlineb uses the environment to store positional parameters. Alternatively, there's also an integrated substitution mechanism that doesn't make use of the environment at all.

Current limitations

execlineb builds and executes a unique argv with the script: hence scripts are subject to OS-dependent limitations such as the kernel buffer size for argv and envp - at least 64 kB on most systems. This means that execlineb cannot execute arbitrarily large scripts. Be careful with deeply nested scripts too: without the -p/-P/-S/-s option, each execlineb invocation uses up some space in the environment.