Bash function script

Question

I am having a lot of difficulties with one of my homework assignments and was wondering if I could get some help on this.

Here are the instructions

1.Sets an alias for the less command so that it will display line numbers when l is used and the filename is passed:
       a. Ex: l filename
2.Reads the   /etc/passwd  file, use the variable Line to store the data
3.Uses a function to process the data read from /etc/passwd
       a. Use the global variable, Line, when processing the data
       b. Information passed to the function from the main script is:
              1)The username field number
              2)The UID field number
       c. The function will determine which UIDs are less than 100 and then write those to a file named           results.hw5.txt in the user’s home directory
              i.use the form: user’s ID = UID /// user’s name = username
                     ii.Ex: user’s ID = 0 /// user’s name = root
       d.Any variables created within the function must be local.
4.Uses the alias created in Step 1 to read results.hw5.txt

Here is what I have so far.

#!/bin/bash

function func1
{
local filename=/etc/passwd
local results=~/My_Scripts/results.hw5.txt
while IFS=: $line -p uid _ user _ 
do
((uid<=100)) && echo "user id = $uid /// username = $user" > $results
done < $filename
}
alias l='less'
line=$(read)
func1
l $results

You need something like while read Line; do ...; done < /etc/passwd outside the function. — Barmar
– Barmar, Commented Dec 13, 2016 at 2:14
The function is supposed to take the username and UID as parameters. — Barmar
– Barmar, Commented Dec 13, 2016 at 2:15
So you need to read the line into Line in the loop, then extract the username and UID from this, then call func1 $username $uid — Barmar
– Barmar, Commented Dec 13, 2016 at 2:16

tripleee · Accepted Answer · 2017-12-26 10:07:04Z

while IFS=: $line -p uid _ user _ do

This contains multiple errors. $line can't be expected to be a valid command and the -p option to read requires an argument (if that is even what the -p is for here).

The instructions to create an alias are misdirected, but the apparent lesson here is that you can include an option in the alias definition.

alias l=`less -option`

(I'm not giving away the precise option to use here. Look it up.)

Your specification says to process each passwd entry inside the loop. So the loop needs to look something like

while read -r line; do
    funcname  # argument "$line" is global implicit
done</etc/passwd

The guidance to use a global variable to pass information to the function is also highly dubious.

The parsing of line should happen inside the function - again, a doubtful design, but here goes.

funcname () {  # prefer POSIX function definition syntax
    # split on colons into positional parameters
    local IFS=:
    set -- $line
    # now, $1 is account name, $2 is UID, etc
    :
}

I'm not sure how to interpret the instruction to pass field numbers as parameters to the function. Maybe it wants $1 and $2 to be parameters you can pass in to identify which fields to extract? (Hint: ${$var}. And you obviously need to capture the function arguments before overwriting the positional parameters with set.)

As an aside, you are violating the instructions by not writing the file into the user's home directory. Maybe omit the My_Scripts subdirectory.

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