Extracting values from files

Master Error · #1 (**permalink**) 08-13-2004

Im trying to create a utility that can do unit conversions using a seperate formula file(one which i can add conversions to at a later date). however i'm stuck when it comes to pulling the formulas out of the formula file for use in the script.
heres a rundown of what the script does.

The formula file consists of 3 columns :
a code such as m_ft (metres to feet), the constant (used for the conversion), and a description

In the script the user types in the code (m_ft for example), the script then searches for the code in the formula file (using grep).. i opted to send the output from grep into a temp file.
problem is now i want to extract the 2nd column that contains the constant for use in the script. Is there a way to cut the constant and put it into a variable in the script, and then apply an arithmetic operation to it ( y = x * constant) ?

I've looked up piping the cut command but no where does it say if i can pipe to a variable and how the variable will behave.

Tnx

MacMonster · #2 (**permalink**) 08-14-2004

Code:

#!/bin/bash

echo -n "Enter formula code: "
read code

if [ ! `cat formula.txt | cut -d ' ' -f 1 | grep "$code"` ]; then
    echo "No such formula."
    exit
fi

echo -n "Enter value: "
read value

awk '$1 == "'"$code"'" { print '"$value"' * $2 }' formula.txt

Formula.txt is the formula database file. This is the content of my formula.txt:

Code:

hkd_usd  0.128 #HKD -> USD
kg_pound 2.2   #KG  -> Pound
min_sec  60    #Minute -> Second
mile_km  1.6   #Mile -> Kilometer
nm_km    1.852 #Nautical mile -> Kilometer

Master Error · #3 (**permalink**) 08-14-2004

Thats great

but if u don't mind could u break that down for me so i can understand what the codes are doing ...

just these two steps

Quote:

if [ ! `cat formula.txt | cut -d ' ' -f 1 | grep "$code"` ];

Quote:

awk '$1 == "'"$code"'" { print '"$value"' * $2 }' formula.txt

sorry still a beginner, so id much rather learn then copy..

google · #4 (**permalink**) 08-14-2004

quote:
--------------------------------------------------------------------------------
if [ ! `cat formula.txt | cut -d ' ' -f 1 | grep "$code"` ];
--------------------------------------------------------------------------------

The code above uses the 'cat' command to pass the contents of the formula.txt file to the 'cut' command. The cut command is used to the cut out the first field ( this is the -f 1 portion of the command) within the file. Each field is delimited by 'cut' by a space (this is the -d ' ' portion of the command). Finally, the output of the cut command (that is, the first field) is passed to 'grep' which then attempts to match one of the entries in the file. Code is set to a value passed in by the user. This whole command sequence is surrounded by a file test which is testing whether or not 'grep' found a match. If it doesnt, the program exits and a message is printed to the screen. "No such formula"

quote:
--------------------------------------------------------------------------------
awk '$1 == "'"$code"'" { print '"$value"' * $2 }' formula.txt
--------------------------------------------------------------------------------
This peice of code searches for the entry in the formula.txt file that matches what the user typed in (I assume this is a value such as USD, or Pound, or Second etc). Awk will then match the entry and use the value (another peice of data entered by the user) multiplied by the second field ($2) of the record matched. The output of this step is printed to the screen.

A few thoughts, it would be better to use a "Select case" to generate a menu rather than have the user type in something that may not be in the file. Also, when using Awk, it would be more portable to use the built in -v switch to pass in shell variables to the program.

Master Error · #5 (**permalink**) 08-15-2004

Hey thnx ... gonna experiment a bit now...

sure glad i found this forum..

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