How does the while Read loop in shell work?
Here, catreads each line from standard input and writes the line to standard output. It continues until the end-of-file condition is reached on file1, then it stops. In shell programming, we can read a line from standard input using the readcommand. The readcommand succeeds so long as a line can be read.
When to use the ” while ” loop in programming?
The “While” Loop. A “While”. Loop is used to repeat a specific block of code an unknown number of times, until a condition is met. For example, if we want to ask a user for a number between 1 and 10, we don’t know how many times the user may enter a larger number, so we keep asking “while the number is not between 1 and 10”.
How to use while Read loop in AWK?
Then i have this while read loop to compare one of the columns to a number then echo something. However, instead of echoing my desired phrase, it echoes something else. instead of echoing the above, it echoes the 2nd column of the file. for a mixed awk/bash solution.
How to use while read in Linux stack exchange?
Also, alternatively, you could pipe the output of the command directly to the while loop instead: < /home/dir/file.txt awk ‘ {print $2}’ | while read num. Thanks for contributing an answer to Unix & Linux Stack Exchange!
How to read from the console while looping over?
Take a simple example like this: You may (wrongly!) expect this to loop over each matched line, and allow the user to press on each match. It will NOT provide the user a chance to respond because the input of read will come from the output of the initial command.
Is there a way to read from standard input?
In shell programming, we can read a line from standard input using the read command. The read command succeeds so long as a line can be read. If the input reaches end-of-file, however, the next read fails. This is exactly what happens in the cat command.
When to take input inside a while loop in Bash?
If you are using the direct output of a command to feed a while loop in BASH, you may still want to take user input inside that loop. For example, if you need the user to confirm each line by pressing . Take a simple example like this: