read from stdin in a shell script

bujecas · 02-02-2006, 09:53 AM

Hello,
I want to write a shell script that can be used in a pipe. For example,

cat test.txt | script.sh

The script.sh should be feeded by the output of cat.

I couldn't find out how to do it. Any ideias? Thanks.

haertig · 02-02-2006, 10:28 AM

In the example below, "ttt" is a two line text file and "qqq" is the shell script that accepts input from that file. "qqq" illustrates reading an entire line from stdin and also parsing a line into individual parameters.

Code:

$ cat ttt
The entire line
1 2 3


$ cat qqq
echo
x=`line`
echo "I read the first line as:"
echo "<$x>"
echo
read a b c
echo "I parsed the second line as:"
echo "1st param: <$a>"
echo "2nd param: <$b>"
echo "3rd param: <$c>"
echo


$ cat ttt | qqq

I read the first line as:
<The entire line>

I parsed the second line as:
1st param: <1>
2nd param: <2>
3rd param: <3>

$

pixellany · 02-02-2006, 12:51 PM

A few general comments:
A script is not fed by stdin---rather the COMMANDS work off of stdin.
If you run a script from a terminal, then the first command that needs input will expect it from the terminal unless you use redirection to tell it other wise. If you do not run from a terminal, then I think stdin is ambiguous and you need explicit redirection.

More detailed answer might be easier with an example of what you want to do.

disem · 07-03-2009, 04:46 PM

keep it simple people..

Code:

#!/bin/sh
# Converts all lowercase text from
# stdin to uppercase
#
tr '[:lower:]' '[:upper:]' < /dev/stdin

# edward
# ebaddouh@gmail.com

you should call your script as follow:

Code:

$ echo "keep it simple" | myscript.sh
KEEP IT SIMPLE

cheers