How do I print a number with bash for shell script?

Question

Sorry this is a very easy question, how do I print 0 from a shell script? My program is doing scanf for a number, I want the script to enter 0.

I tried echo 0, it doesnt seem to work.

#!/bin/bash
make clean
ls -l
cat udpserver.c
make
ls -l
./udpserver
sleep 2
echo 0 | udpserver
sleep 2
echo 0 | udpserver

@BenjaminW. See his edited question, it's not as simple as the duplicate. — Barmar
– Barmar, Commented May 4, 2017 at 1:35

Barmar · Accepted Answer · 2017-05-04 01:29:15Z

3

You can't use a pipe to send input to a program that you started previously, you have to use it when starting the program. If you want to pipe multiple commands to it, put them in a subshell.

(sleep 2; echo 0; sleep 2; echo 0) | ./udpserver

edited May 4, 2017 at 1:29

answered May 4, 2017 at 1:10

Barmar

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7 Comments

paxdiablo Over a year ago

Or ( echo line1 ; echo line2 ) | yourProg or printf "line1\nline2\n" | yourProg - the possibilities are almost endless :-)

Barmar Over a year ago

@paxdiablo I didn't mention that because I said that using a here-doc is best for multiple lines.

sublimesummer Over a year ago

I dont get it, where am I going wrong here? Heres my script:

Barmar Over a year ago

@sublimesummer Don't put code in comments. Edit your question to show what you tried.

paxdiablo Over a year ago

Barmar, wasn't criticising your answer (in fact I voted for it), but there are situations where a heredoc doesn't cut it. Specifically, if the input has to be more complex, such as ( expr $bytes / 1024 ) | processKilobytes. The OPs question is nowhere near that level of complexity as you rightly point out.

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