bash create array of ids for launching processes - bash

Question

I have to come up with an array of values. They're going to represent the server and/or virtual server ids they'll represent. So I have to run 100 application instances on 25 servers.
server 1 runs process 1,26,51,76
server 2 runs process 2,27,52,77
...
server 25 runs process 25,50,75,100
I need a way to execute the scripts like this
# hostname is in a format like production-01.localdomain
host_id=`hostname | tr 'A-Za-z-.' ' ' | tr -d '[[:space:]]'`
# need to create array of server ids in server_ids
for server_id in server_ids
do
/usr/local/bin/virtual_process $server_id
done
but I don't know how to create the server_ids array. Help!

Answer 1

here ya go. This solves your problem by creating a space separated string instead of an array which would be overkill
# hostname is in a format like production-01.localdomain
server_id=`hostname | tr 'A-Za-z-.' ' ' | tr -d '[[:space:]]' | awk '{print NR}'`
# need to create array of server ids in server_ids
server_ids="$server_id $(( $server_id+25 )) $(( $server_id+50 )) $(( $server_id+75 ))"
for server_id in $server_ids
do
/usr/local/bin/virtual_process $server_id
done

Answer 2

Here's an idiomatic Bash solution that should work as-is:
#!/usr/bin/env bash
# Extract the base server ID by extracting the number from the hostname,
# eliminating any leading zeros.
# E.g., 'production-01.localdomain' -> '1'
baseServerId=$(( 10#$(tr -dC '[0-9]' <<<"$HOSTNAME") ))
# Loop 4 times, starting with the base server ID and
# adding 25 in each subsequent iteration.
for (( i = 0; i < 4; ++i )); do
/usr/local/bin/virtual_process "$(( baseServerId + i * 25 ))"
done
As you can see,
A single tr command utilizing -C for the complement is enough to extract digits only: -dC '[0-9]' means: delete (-d) everything but (-C) digits ([0-9]).
Since the resulting number can have leading zeros, these must be removed to avoid misinterpretation as an octal number. Evaluating the tr command inside an arithmetic expansion $(( ... )) with 10# - the desired number base - prepended to the output from tr, does just that.
No need for an array of server IDs when an arithmetic, C-style loop will do.
That said, since the list of offsets is so small and has fixed increments, a more succinct solution is:
for offset in 0 25 50 75; do
/usr/local/bin/virtual_process "$(( baseServerId + offset ))"
done
A more algorithmic approach using brace expansion (which, it should be noted, only supports literal arguments; Bash v4+ is required due to using a 3rd argument to specify a step value):
for offset in {0..75..25}; do
/usr/local/bin/virtual_process "$(( baseServerId + offset ))"
done

Answer 3

If you just need a sequence of numbers from 1 to 25 you can use bash's brace expansion.
for server_id in {1..25}
do
/usr/loca/bin/virtual_process $server_id
done