Convert Perl to Shell - perl

Question

I have Perl script that I use to SNMP walk devices. However the server I have available to me does not allow me to install all the modules needed. So I need to convert the script to Shell (sh). I can run the script on individual devices but would like it to read from a text like it did in Perl. The Perl Script starts with:
open(TEST, "cat test.txt |");
#records=<TEST>;
close(TEST);
foreach $line (#records)
{
($field1, $field2, $field3)=split(/\s+/, $line);
# Run and record SNMP walk results.

Answer 1

Depending on exactly what the input is and what you are trying to do, that perl code fragment would likely translate to:
while read field1 field2 field3
do
# Run and record SNMP walk results.
echo "1=$field1 2=$field2 3=$field3"
done <text.txt
For example, if text.txt is:
$ cat text.txt
one two three
i ii iii
Then, the above code produces the output:
1=one 2=two 3=three
1=i 2=ii 3=iii
As you can see, the shell read command reads a line (record) at a time and also does splitting on whitespace. There are many options for read to control whether newlines or something else divide records (-d) and whether splitting is to be done on whitespace or something else (IFS) or whether backslashes in the input are to be treated as escape characters or not (-r). See man bash.

Answer 2

while read string; do
str1=${string%% *}
str3=${string##* }
temp=${string#$str1 }
str2=${temp%% *}
echo $str1 $str2 $str3
done <test.txt
alternate version
while read string; do
str1=${string%% *}
temp=${string#$str1 }
str2=${temp%% *}
temp=${string#$str1 $str2 }
str3=${temp%% *}
echo $str1 $str2 $str3
done <test.txt
POSIX substring parameter expansion
${parameter%word}
Remove Smallest Suffix Pattern. The word shall be expanded to produce
a pattern. The parameter expansion shall then result in parameter,
with the smallest portion of the suffix matched by the pattern
deleted.
${parameter%%word}
Remove Largest Suffix Pattern. The word shall be expanded to produce a
pattern. The parameter expansion shall then result in parameter, with
the largest portion of the suffix matched by the pattern deleted.
${parameter#word}
Remove Smallest Prefix Pattern. The word shall be expanded to produce
a pattern. The parameter expansion shall then result in parameter,
with the smallest portion of the prefix matched by the pattern
deleted. ${parameter##word} Remove Largest Prefix Pattern. The word
shall be expanded to produce a pattern. The parameter expansion shall
then result in parameter, with the largest portion of the prefix
matched by the pattern deleted.
${parameter##word}
Remove Largest Prefix Pattern. The word shall be expanded to produce a
pattern. The parameter expansion shall then result in parameter, with
the largest portion of the prefix matched by the pattern deleted.