shell script to map fields and return the corresponding value from list

Question

Symbol  Test  
XXX,1  
GHL,2  
MKT,13  
LOC,15  
LMT,76  
TIF,45  

Shell script should return corresponding symbol for each Test.

If $Test=1,then $symbol should be XXX

how can I achieve this?

Answer 1

You can use bash associative array :

declare -A foobar
while read -r foo bar; do foobar["$bar"]="$foo"; done < <(tail -n +2 file.txt)

This will generate an associative array named foobar by reading the lines starting from second line from the file containing the key-value mapping.

Now you can declare a small function like :

choose () { echo "${foobar["$1"]}" ;}

It will output the value stored on the specified key given as first argument.

Example :

$ choose 2
GHL
$ choose 1
XXX

Answer 2

This just needs a little bit of awk:

awk -v var=1 '$2 == var {print $1}' your_file

That is, look for the lines having the 2nd field equal to the given variable var; when this happens, print the first field.

Answer 3

Python can do the job too:

python -c 'import sys;print [i.split(",")[0] for x,i in enumerate(sys.stdin) if x > 0 and i.strip().split(",")[1] == sys.argv[1]]' 13  < input.txt

Or as actual script:

#!/usr/bin/env python
import sys
for x,i in enumerate(sys.stdin): 
    if x > 0 and i.strip().split(",")[1] == sys.argv[1]:
         print i.strip().split(",")[0]

Test run:

$ python find_line.py 76 < input.txt                                                                                         
LMT

The way this works is simple: we redirect input.txt into script's stdin and then read it line by line, skipping first line and splitting lines into list using comma. The desired number to look up is given as first command-line argument.

It would make much easier if there wasn't the header line - that would eliminate enumerate() call, and simplify line check to if i.strip().split(",")[1] == sys.argv[1]