Igor's Blog
Programming, DIY, Games, Hacks, and Tech

I've been having to write more than my usual share of shell scripts lately that orchestrate a number of other command line utilities and other shell scripts. Some of the scripts I've had to run from my script behaved well but some required user input and did not give any options to provide that input as command line arguments. Since I was not able to modify the scripts that I was calling, I had to find a different way to invoke them.
bash_read1.png


The scripts that I was calling used the 'read' command to prompt the user for input like so:
 External Script
read -p "Please enter input 1: " my_var1
read -p "Please enter input 2: " my_var2
read -p "Please enter input 3: " my_var3


These were interactive scripts but with a predictable pattern for input. Luck was on my side and I knew what each of these inputs should be while my script was being run. All I had to do was provide this input so that the external script would run as if it were a non-interactive script.

There are a number of ways to do the above, I went for something really simple, using echo and piping its output to the external script, like so:
 My Script
echo "MyInput1
MyInput2
MyInput3
" | external_script.sh


Note that the echo string is split across multiple lines, this is completely OK to do. Also note that after my 3rd input value there is a new line, that is because I needed that final return character since the 'read' command in the external script would be expecting that.

The same approach worked when the external script prompted for a password using 'read -s' too.

The above approach worked really well in my case, but it's not suitable for every occasion. In more complex situations the 'expect' command would do a better job, but I'll leave that for another article.



-i

comments powered by Disqus
Other posts you may like...

Recent Blog Posts

A hack to create an uber jar with the Maven Shade Plugin using local jar files

Is it worth it? Apple USB-C Digital Multi AV adapter vs a cheap eBay clone

Running X11 graphical applications after changing to another user using 'sudo su'

How to stop Facebook using ad images as post sharing thumbnails

Picking lists for Atari Lynx capacitor replacement kits

Performance - 2012 Retina MacBook Pro vs 2017 MacBook Pro

Look and feel - 2012 Retina MacBook Pro vs 2017 MacBook Pro

Using math to work out the diameter of hard to reach water cooling pipes

How to get the unreachable shard in the Hinterlands in DragonAge Inquisition

Measy RC12 wireless 2.4Ghz keyboard touchpad review

Recent Galleries

Monument Valley 2 is released and does not disappoint

Space Food - Chocolate Ice Cream with Chocolate Chips

Legeod Star Wars AT-DP kit

DIY spare parts computer build with a RAIDMAX Anura case

Fake 'Lepin' brand Lego packaging

Hardwood garden bench with clear resin void filler

Fixing a 3D printer extruder that stopped heating up

Easily increase disk space in a Lenovo Ideapad 100S 14" laptop with an M.2 SSD

Making a multi-piece 3D printed solder spool holder stand

DIY indoor apartment grow light wiring

My Other Web Sites

Igor and Elise's Travels
Riverside Expressway Cam
300 George St Blogumentary

My Online Tools

UUID to OID Converter
Guru JSON-RPC Tester
Extrudifier Object Designer
Travel ┬ÁBlog

Blogs and Friends

Matt Moores Blog
Georgi's FlatPress Guide
Perplexing Permutations
The Security Sleuth
Ilia Rogatchevski
Travelling Fairy

Blog Activity

Blog Activity
Don't forget to
me for more great articles!
Don't show this again