Avoiding temporary files while iterating over pipeline results - bash

Question

I've created the function to display interfaces and IP's per interface
network() {
iplst() {
ip a show "$i" | grep -oP "inet\s+\K[\w./]+" | grep -v 127
}
ip ntable | grep -oP "dev\s+\K[\w./]+"| grep -v lo | sort -u >> inf_list
netlist="inf_list"
while read -r i
do
infd=$i
paste <(echo -e $i) <(iplst)
done < $netlist
}
Current output:
ens32 10.0.0.2/24
10.0.0.4/24
10.0.0.20/24
ens33 192.168.1.3/24
ens34 192.168.0.2/24
ens35 192.168.2.149/24
but would like to avoid creation of temp files,
would appreciate suggestions

Answer 1

In general, temporary files can be replaced with process substitution. For instance, to avoid the inf_list temporary file, one can generate its contents with an inf_list function:
build_inf_list() {
ip ntable | grep -oP "dev\s+\K[\w./]+"| grep -v lo | sort -u
}
iplst() {
ip a show "$1" | grep -oP "inet\s+\K[\w./]+" | egrep -v '^127'
}
while read -r i; do
paste <(printf '%s\n' "$i") <(iplst "$i")
done < <(build_inf_list)
Some notes:
Passing (and using) explicit arguments makes it much more obvious to a reader than relying on globals set elsewhere in your code, and reduce the chances that functions added in the future will stomp on variable names you're depending on.
Using process substitution, <(...), is replaced with a filename which, when read from, will return the stdout of the command ...; thus, since what you're writing to your temporary file comes from such a command, you can simply replace the temporary file with a process substitution invocation.
Any shell where echo -e does not print -e on its output is defying black-letter POSIX. While bash is noncompliant in this manner by default, it's not noncompliant consistently -- if the posix and xpg_echo flags are both set, then bash complies with the letter of the standard. It's much safer to use printf, which is far more robustly defined. See also the APPLICATION USAGE and RATIONALE sections of the linked standard document, which explains how BSD and AT&T UNIX have traditionally incompatible versions of echo, and thus why the POSIX standard is so loose in the behavior it mandates.

Answer 2

Final result, thanks #Charles Duffy
#!/bin/bash
build_inf_list() {
ip ntable | grep -oP "dev\s+\K[\w./]+"| grep -v lo | sort -u
}
iplst() {
if [ "$1" = "lo" ]; then
ip a show "$1" | grep -oP "inet\s+\K[\w./]+" | grep -v '^127'
else
ip a show "$1" | grep -oP "inet\s+\K[\w./]+"
fi
}
while read -r i; do
paste <(printf '%s\n' "$i") <(iplst "$i")
done < <(build_inf_list)
edited