CODEWITHSUNDEEP
shellshbusybox
Vamsi
Vamsi

Reputation: 87

Process Substitution to named pipe conversion

I am new to Busybox and I found that process substitution don't work in Busybox. Can anyone help me to emulate below command in Busybox using named pipe.

cat <(echo 0 0 1 /config/camConfig.txt 0 3840 2160 8 0 0) - | ~/tools/camera/stream

I am developing a camera which runs on Busybox. In order to stream camera for analysis I need to start an application /tools/camera/stream, but every time I run this application I need to insert same set of information to the application manually, then it will start stream, after analysis is complete I need to enter number 13 in application to stop camera. So I want to automate this task and I tried above command. Later I found that I cannot do this. I tried the below command but only the first input 0 is passed to application.

[ -p ~/config/settings.txt ] || mkfifo ~/config/settings.txt
echo 0 0 1 /config/camConfig.txt 0 3840 2160 8 0 0 > ~/config/settings.txt &
cat <~/config/settings.txt - | ~/tools/camera/stream

Please help me to find a solution.

Upvotes: 1

Views: 453

Answers (1)

John Kugelman
John Kugelman

Reputation: 361729

<(...) is a Bash-ism and Busybox only supports plain sh syntax. An sh-compatible way to do this is to run echo and cat in within curly braces and pipe the resulting compound command to your tool.

{ echo 0 0 1 /config/camConfig.txt 0 3840 2160 8 0 0; cat; } | ~/tools/camera/stream

I would do this even in Bash as it's a more direct and thus more efficient expression of what you're trying to do.

For what it's worth, I think your solution would work if you removed the < redirection from the final line.

cat ~/config/settings.txt - | ~/tools/camera/stream

Why not use <? You're trying to cat both a pipe and stdin. If you use < that causes settings.txt to be redirected to stdin, which conflicts with the - and means stdin is no longer connected to the keyboard.

Also, I'd probably stick the pipe in /run, which is for ephemeral runtime files—perfect for pipes. (Or, alternatively, /var/run or /tmp.) And I'd give it a .fifo extension to indicate it's not a regular file.

Upvotes: 2

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