Running System Commands

Julia does not send system commands to a shell as described in the manual

This has a number of concequences:

File-names etc do not need to be escaped if parsed as an interpolated variable
Commandline options are not split on space if parsed as an interpolated variable
Piping and redirection using shell constructs like "|" and ">" do not work.
stdin and stderr are not collected by default.

Basic usage

Simply running a command is a combination of backticks and run():

o1 = run(`ls -lrt .`)

however, the output of the command is not collected:

julia> o1
Process(`ls -lrt .`, ProcessExited(0))

To redirect stdin and stdout to files, a pipeline is needed:

run(pipeline(`ls -lrth .`, stdout = "/tmp/o1", stderr="/tmp/e1"))

Passing multiple options in a string does not work:

julia> o1 = "-l -r"
"-l -r"

julia> run(`ls $o1 .`)
ERROR: failed process: Process(`ls '-l -r' .`, ProcessExited(2)) [2]

The individual options need to be given as a vector

o2 = split("-l -r")
run(`ls $o2 .`)

The equivalent of a shell pipeline is the command pipeline():

run(pipeline(`ls $o2`, `sort -g`))

As noted above, the pipeline command (not run) takes keyword arguments stdin and stdout to re-direct the output.

run(pipeline(pipeline(`ls $o2`, `sort -g`), stdout = "/tmp/o1"))