Manually iterating a line of a file | bash

Question

I realize I could do this in any other language - but with Bash - I've looked far and wide and could not find the answer.

I need to manually increase $line in a script: Example:

for line in `cat file`
do
foo()
       foo_loop(condition)
{
 do_something_to_line($line) 
}
done

If you notice, every time the foo_loop iterates, $line stays the same. I need to iterate $line there, and make sure the original for loop only runs the number of lines in file.

I have thought about finding the number of lines in file using a different loop and iterating the line variable inside the inner loop of foo().

Any ideas?

Answer 1

Instead of using a for loop to read through the file you should maybe read through the file like so.

#!bin/bash

while read line
do
    do_something_to_line($line)
done < "your.file"

Answer 2

Long story short, while read line; do _____ ; done

Then, make sure you have double-quotes around "$line" so that a parameter isn't delimited by spaces.

Example:

$ cat /proc/cpuinfo | md5sum
c2eb5696e59948852f66a82993016e5a *-

$ cat /proc/cpuinfo | while read line; do echo "$line"; done | md5sum
c2eb5696e59948852f66a82993016e5a *-

Second example # add .gz to every file in the current directory: # If any files had spaces, the mv command for that line would return an error.

$ find -type f -maxdepth 1 | while read line; do mv "$line" "$line.gz"; done

Answer 3

Sorry for being so vague.

Here we go:

I'm trying to make a section of my code execute multiple times (parallel execution)

Function foo() # Does something
for line in `cat $temp_file`;
foo($line)

That code works just fine - because foo is just taking in the value of line; BUT if I wanted to do this:

Function foo() # Does something
for line in `cat $temp_file`;
while (some condition)
foo($line)
end

$line will equal the same value throughout the while loop. I need it to change with the while loop - then continue when it goes back to the for.

Example:

line = Hi
foo{ echo "$line" }; 
for line in `cat file`;
while ( number_of_processes_running -lt max_number_allowed)
foo($line)
end

If the contents of file were

"Hi \n Bye \n Yellow \ Green \n"

The output of the example program would be (if max number allowed was 3) Hi Hi Hi Bye Bye Bye Yellow Yellow Yellow Green Green Green.

Where I want it to be Hi Bye Yellow Green

I hope this is better - I'm doing my best to explain my problem.

Answer 4

You should post follow-ups as edits to your question or in comments rather than as an answer.

This structure:

while read line
do
    for (( i=1; i<$max_number_allowed; i++ ))
    do
        foo $line
    done
done < file

Yields:

Hi
Hi
Hi
Bye
Bye
Bye
...etc.

While this one:

for (( i=1; i<$max_number_allowed; i++ ))
do
    while read line
    do
        foo $line
    done < file
done

Yields:

Hi
Bye
Yellow
Green
Hi
Bye
Yellow
Green
...etc.