Bash: read a file line-by-line and process each segment as parameters to other prog

Question

I have some dirty work to do, so a Bash script seems to be a good choice. I'm new to Bash, and the experience makes me kind of frustrated.

The file mapfiles.txt consists of lines as follow. Each line has four segments separated by a white space. Each segment represents a input parameter to an external program name 'prog'. For example, "cm19_1.png" is the filename, "0001" the index, "121422481" the longitude, and "31035995" the latitude.

File: mapfiles.txt

cm19_1.png 0001 121422481 31035995
cm19_2.png 0002 121423224 31035995
cm19_3.png 0003 121423967 31035995
…

I want to execute similar commands to each line. As show below, the prog's input parameter order is slightly different. So it makes sense to write a bash script to handle the repeated work.

[Usage] prog <index> <longitude> <latitude> <filename>
example: prog 0001 121422481 31035995 cm19_1.png

Generally, the bash script will operate in this way:

1. Read one line from mapfiles.txt
2. Split the segments
3. Call the prog with a correct parameter order

Here comes run.sh.

#!/bin/sh

input=mapfiles.txt
cmd=prog

while read line
do
        file=$(echo $line | cut -d' ' -f1)
        key=$(echo $line | cut -d' ' -f2)
        log=$(echo $line | cut -d' ' -f3)
        lat=$(echo $line | cut -d' ' -f4)
        echo $cmd $key $log $lat $file
done < "$input"

What I expected is

prog 0001 121422481 31035995 cm19_1.png
prog 0002 121423224 31035995 cm19_2.png
prog 0003 121423967 31035995 cm19_3.png
… 

The ACTUAL result I got is

 cm19_1.png21422481 31035995
 cm19_2.png21423224 31035995
 cm19_3.png21423967 31035995

Problems that confused me

1. Where is 'prog'?
2. Where is the white space?
3. What's wrong with the parameter order?

Hmm… I wrote this script on my Mac using vim and copy it to a Scientific Linux box and a gentoo box. These three guys get the same ridiculous outputs.

question from:https://stackoverflow.com/questions/7619438/bash-read-a-file-line-by-line-and-process-each-segment-as-parameters-to-other-p

Answer 1

You can simplify this a lot:

while read file key log lat
do
  echo "$cmd" "$key" "$log" "$lat" "$file"
done < "$input"