Shell Tricks¶
How to Execute Two Processes in Parallel¶
We want to ping two machines parallel. Kapow! can get IP addresses from query params:
1 2 3 4 5 6 7 | $ cat parallel-route #!/usr/bin/env sh kapow route add '/parallel/{ip1}/{ip2}' - <<-'EOF' ping -c 1 -- "$(kapow get /request/matches/ip1)" | kapow set /response/body & ping -c 1 -- "$(kapow get /request/matches/ip2)" | kapow set /response/body & wait EOF |
Calling with curl:
1 | $ curl -v http://localhost:8080/parallel/10.0.0.1/10.10.10.1 |
Script debugging¶
Bash provides the set -x
builtin command that “After expanding each simple command,
for command, case command, select command, or arithmetic for command, display the
expanded value of PS4, followed by the command and its expanded arguments or associated
word list”. This feature can be used to help debugging the init programs and,
together the --debug
option in the server sub-command, the scripts executed
in user requests.