Make Shellscript act as pipLine

Question

How can I get my script to act in a pipeline

example:

ls|./meuScript|grep 'Mensagem Qualquer'

what './meuScript' has to have to act as a filter ?

Answer 1

Just have your script use commands that read the default input and write to the default output.

Example:

We have the script abc-lines.sh:

#!/bin/bash
grep abc | wc -l

We can use it in this command:

$ echo -e 'abcd\nefgh\n123abc\nxabcy\nzzz' | \
./abc-lines.sh | \
sed -r 's/(.*)/[\1]/'

...and the result will be: [3]

This is because the default input of your script commands will be the default input of your script (unless the command is after a pipe, such as wc example). The same goes for functions.

If you need to capture the standard input for more elaborate manipulations you can use the read. Example:

#!/bin/bash
while read LINE
do
    echo "I read $LINE"
    # alguma mágica aqui
done

Anything you print, be with echo or any other command, may be used by another script in the sequence of user-made Pipes.

Warning: There are two STDOUT and STDERR outputs. The pipe will transmit to STDOUT.

If you want to send the output of a command to STDERR to escape the PIPE, do:

echo "mensagem de erro" >&2

If you want to merge STDERR with STDOUT to pipette both of you, do:

ls /nowhere 2>&1 | grep something