Scripting : Dual line output into next script as variables

facets · 06-09-2004, 11:44 PM

Hey all,

I have a script which outputs a two line answer to stdin :
1
2

I need to be able to pick these up and set variables for another script with them.

Any ideas on how I could achieve this?

Cheers, mark.

pcardout · 06-10-2004, 12:29 AM

I think bash scripts suck for lots of things (I keep thinking to myself a REAL programming language wouldn't make you do this ... Thus Python).

You can still do it though. Maybe the real gurus have a more elegant approach. This works though. It's excerpts from a script
in which I want to do calculations on the output of the date
command (basically timing upload and download across a network on a regular basis).

File=~/temp1 #create a junk temporary file
date +%s >$File #Redirect seconds since 1970 to junk file
#Run some commands that waste time
# Now check the time again
date +%s >$File #Redirect seconds since 1970 to junk file
# Now check the time again
date +%s >$File #Redirect seconds since 1970 to junk file
#So the file 'temp1' now contains three lines. Let's say I want
# to know the difference in time between those three times.
{
read time1
read time2
read time3
} < $File

let delta1=$time2-$time1; let delta1=1000/$delta1
echo 'download 1 KBYTE' $delta1 'bytes/s'
let delta2=$time3-$time2; let delta2=500000/$delta2

Dark_Helmet · 06-10-2004, 01:28 AM

If the first script is going to send data to stdout, and the next script is going to take it as stdin (in other words, there's going to be a pipe in here somewhere), why not just you temporary environment variables?

At the end of the first script:

Code:

temp_transfer_var1=value of output line 1
temp_transfer_var2=value of output line 2

export temp_transfer_var1 temp_transfer_var2

Near the beginning of the second script:

Code:

internal_var1=${temp_transfer_var1}
internal_var2=${temp_transfer_var2}

unset temp_transfer_var1 temp_transfer_var2

==============

Another way is to do a classic "while read" (again, assuming the command structure is: script1 | script2)

Code:

internal_var1=""
internal_var2=""

while read output_line ;
do
  if [ "${internal_var1}x" = "x" ] ; then
    internal_var1=${output_line}
  else
    internal_var2=${output_line}
  fi
done

pcardout · 06-10-2004, 01:38 AM

I like Dark helmet's export of environment variables. Hadn't figured
out how to do that. I want Dark Helmet to know that I think he's a real space ball, and I mean that in a good way.

Dark_Helmet · 06-10-2004, 11:36 AM

Making environment variables is similar to solving a scope-issue in a programming language by making a variable global. It's usually not the best way to go about things, but it's quick. If the environment variables are used, please pick some long/obscure name to avoid potentially trashing a variable put in place by the system. It would be very unwise to assign a new value to HOME or EDITOR for example.

======================

"What's the matter Col. Sanders? Chicken?!?" - Dark Helmet

jim mcnamara · 06-10-2004, 01:30 PM

Assume prog1 outsputs to stdout. prog2 needs two variables - it can read them from stdin.

Code:

prog1 | prog2

first lines of prog2

Code:

#!/bin/bash
read var1 var2

Dark_Helmet · 06-10-2004, 02:28 PM

<sigh />

As per the usual, I made things too difficult. It's a theme I really need to reign in on.