Multiple variables into one variable with wildcard - linux

Question

I have this script:
#!/bin/bash
ping_1=$(ping -c 1 www.test.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//')
ping_2=$(ping -c 1 www.test1.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//')
ping_3=$(ping -c 1 www.test2.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//')
ping_4=$(ping -c 1 www.test3.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//' )
Then I would like to treat the outputs of ping_1-4 in one variable. Something like this:
#!/bin/bash
if [ "$ping_*" -gt 50 ]; then
echo "One ping is to high"
else
echo "The pings are fine"
fi
Is there a possibility in bash to read these variables with some sort of wildcard?
$ping_*
Did nothing for me.

Answer 1

The answer to your stated problem is that yes, you can do this with parameter expansion in bash (but not in sh):
#!/bin/bash
ping_1=foo
ping_2=bar
ping_etc=baz
for var in "${!ping_#}"
do
echo "$var is set to ${!var}"
done
will print
ping_1 is set to foo
ping_2 is set to bar
ping_etc is set to baz
Here's man bash:
${!prefix*}
${!prefix#}
Names matching prefix. Expands to the names of variables whose
names begin with prefix, separated by the first character of the
IFS special variable. When # is used and the expansion appears
within double quotes, each variable name expands to a separate
word.
The answer to your actual problem is to use arrays instead.

Answer 2

I don't think there's such wildcard.
But you could use a loop to iterate over values, for example:
exists_too_high() {
for value; do
if [ "$value" -gt 50 ]; then
return 0
fi
done
return 1
}
if exists_too_high "$ping_1" "$ping_2" "$ping_3" "$ping_4"; then
echo "One ping is to high"
else
echo "The pings are fine"
fi

Answer 3

You can use "and" (-a) param:
if [ $ping_1 -gt 50 -a \
$ping_2 -gt 50 -a \
$ping_3 -gt 50 -a ]; then
...
...
Or instead of defining a lot of variables, you can make an array and check with a loop:
pings+=($(ping -c 1 www.test.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//'))
pings+=($(ping -c 1 www.test1.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//'))
pings+=($(ping -c 1 www.test2.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//'))
pings+=($(ping -c 1 www.test3.com | tail -1| awk '{print $4}' | cut -d '/' -f 2 | sed 's/\.[^.]*$//' ))
too_high=0
for ping in ${pings[#]}; do
if [ $ping -gt 50 ]; then
too_high=1
break
fi
done
if [ $too_high -eq 1 ]; then
echo "One ping is to high"
else
echo "The pings are fine"
fi

Answer 4

To complement the existing, helpful answers with an array-based solution that demonstrates:
several advanced Bash techniques (robust array handling, compound conditionals, handling the case where pinging fails)
an optimized way to extract the average timing from ping's output by way of a single sed command (works with both GNU and BSD/macOS sed).
reporting the servers that either took too long or failed to respond by name.
#!/usr/bin/env bash
# Determine the servers to ping as an array.
servers=( 'www.test.com' 'www.test1.com' 'www.test2.com' 'www.test3.com' )
# Initialize the array in which timings will be stored, paralleling the
# "${servers[#]}" array.
avgPingTimes=()
# Initialize the array that stores the names of the servers that either took
# too long to respond (on average), or couldn't pe pinged at all.
failingServers=()
# Determine the threshold above which a timing is considered too high, in ms.
# Note that a shell variable should contain at least 1 lowercase character.
kMAX_TIME=50
# Determine how many pings to send per server to calculate the average timing
# from.
kPINGS_PER_SERVER=1
for server in "${servers[#]}"; do
# Ping the server at hand, extracting the integer portion of the average
# timing.
# Note that if pinging fails, $avgPingTime will be empty.
avgPingTime="$(ping -c "$kPINGS_PER_SERVER" "$server" |
sed -En 's|^.* = [^/]+/([^.]+).+$|\1|p')"
# Check if the most recent ping failed or took too long and add
# the server to the failure array, if so.
[[ -z $avgPingTime || $avgPingTime -gt $kMAX_TIME ]] && failingServers+=( "$server" )
# Add the timing to the output array.
avgPingTimes+=( "$avgPingTime" )
done
if [[ -n $failingServers ]]; then # pinging at least 1 server took too long or failed
echo "${#failingServers[#]} of the ${#servers[#]} servers took too long or couldn't be pinged:"
printf '%s\n' "${failingServers[#]}"
else
echo "All ${#servers[#]} servers responded to pings in a timely fashion."
fi

Answer 5

Yes bash can list variables that begin with $ping_, by using its internal compgen -v command, (see man bash under SHELL BUILTIN COMMANDS), i.e.:
for f in `compgen -v ping_` foo ; do
eval p=\$$f
if [ "$p" -gt 50 ]; then
echo "One ping is too high"
break 1
fi
[ $f=foo ] && echo "The pings are fine"
done
Note the added loop item foo -- if the loop gets through all the variables, then print "the pings are fine".