Question

I try to generate a csv file through a lot of functions like that :

function get_sudo_version {
  sudo -V 2>/dev/null|grep -i "sudo version"
}
sudo_version=$(get_sudo_version)

Function above is a simple example but in some cases i cannot be sure the output is correct.
I would like to know what is the best way to validate the function return one text line only.

I thought about something like that

function validate_output {  
  output=$1; 
  echo $1|grep -q "\n"; 
  echo $?; 
}

mytest="val1
err2
err3"

But it’s obviously not working because the variable does not keep the retrun line character:

echo $mytest
val1 err2 err3

So if someone has a good idea of how i could wirte a generic check function i would be glad.

Thanks

Answer 1

If you have GNU grep, you could simply ensure that grep doesn’t produce more than one line of output in the first place via grep -m 1. Alternatively, use sed '/sudo version/!d;q' instead of grep.

A function that simply checks lines of input while passing them through might look like:

shopt -s lastpipe # if bash

# ksh or bash
validate_output() { 
    (( $(tee >(wc -l) >&2) == 1 ))
} 2>&1

# bash
validate_output2() {
    local lines
    tee /dev/fd/2 | mapfile -tc1 -C '((++lines < 2)) || return; :'
    ((lines))
} 2>&1

get_sudo_version | validate_output || echo failed

Many variations on that possible of course. IMO it’s pretty pointless and shouldn’t be used for something like this. Just design your get_sudo_version so that it guarantees the right results.