I am trying to just echo a command within my bash script code.
OVERRUN_ERRORS="$ifconfig | egrep -i "RX errors" | awk '{print $7}'"
echo ${OVERRUN_ERRORS}
however it gives me an error and the $7 does not show up in the command. I have to store it in a variable, because I will process the output (OVERRUN_ERRORS) at a later point in time. What's the right syntax for doing this? Thanks.
foo="bar | baz"
...is assigning the string "bar | baz" to the variable named foo; it doesn't run bar | baz as a pipeline. To do that, you want to use command substitution, in either its modern $() syntax or antiquated backtick-based form:
foo="$(bar | baz)"
Since your intent isn't clear in the question --
The correct way to store code is with a function, whereas the correct way to store output is in a string:
# store code in a function; this also works with pipelines
get_rx_errors() { cat /sys/class/net/"$1"/statistics/rx_errors; }
# store result of calling that function in a string
eth0_errors="$(get_rx_errors eth0)"
sleep 1 # wait a second for demonstration purposes, then...
# compare: echoing the stored value, vs calculating a new value
echo "One second ago, the number of rx errors was ${eth0_errors}"
etho "Right now, it is $(get_rx_errors eth0)"
See BashFAQ #50 for an extended discussion of the pitfalls of storing code in a string, and alternatives to same. Also relevant is BashFAQ #48, which describes in detail the security risks associated with a eval, which is often suggested as a workaround.
Don't use ifconfig, or grep, or awk for this at all -- just ask your kernel for the number you want:
#!/bin/bash
for device in /sys/class/net/*; do
[[ -e $device/statistics/rx_errors ]] || continue
rx_errors=$(<"${device}/statistics/rx_errors")
echo "Number of rx_errors for ${device##*/} is $rx_errors"
done
Use $(...) to capture the output of a command, not double quotes.
overrun_errors=$(ifconfig | egrep -i "RX errors" | awk '{print $7}')
Your double quotes around RX errors are a problem. Try;
OVERRUN_ERRORS="$ifconfig | egrep -i 'RX errors' | awk '{print $7}'"
To see the commands as they are executing, you can use
set -v
or
set -x
For example;
set -x
OVERRUN_ERRORS="$ifconfig | egrep -i 'RX errors' | awk '{print $7}'"
set +x
eval "$OVERRUN_ERRORS" rather than echo "$OVERRUN_ERRORS", we might be having a different discussion (but it'd also be one about how storing code in strings is a bad practice in general, with lots of references to BashFAQ #50 and BashFAQ #48).
echo. He says 'the $7 does not show up in the command', not 'does not show up in the output'. I don't think my interpretation of that text is unreasonable at all. If he said 'I am trying to run a command', or some such, I would have talked about eval.
$ifconfig?OVERRUN_ERRORSdoes not execute any command as written (OVERRUN_ERRORS="$ifconfig | egrep -i "RX errors" | awk '{print $7}'"). What are you really doing? What doesbash -x the-script.shshow?ifconfig, rather than lifting it directly from sysfs (which is where ifconfig itself gets it from)? Pulling it straight from the source is going to be more reliable in terms of not needing to worry about future changes in ifconfig's output format messing up your script.grepandawk.awk '/RX errors/ { print $7 }'does the work of both in one command.