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I've been trying to create a Bash shell script that would create and alter a file called list. Effectively, my goal with the program is to append names to a list, creating the file with a header (if necessary).

However, the script currently fails at one particular point: Whenever I run the script again, the old name disappears and is replaced by the name that was just entered. How can I solve this?

My script:

#!/bin/bash
#Please sign your name here.

echo "Hi, what's your name?"
read name
echo "Hi $name, welcome to the Linux course!"

echo Course Attendees > list
echo $name >> list

Example of problem:

$ bash list.sh
Hi, what's your name?
Test
Hi Test, welcome to the Linux course!

$ cat list
Course Attendees
Test

$ bash list.sh
Hi, what's your name?
Test2
Hi Test, welcome to the Linux course!

$ cat list
Course Attendees
Test2
Eliah Kagan
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user636667
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1 Answers1

4

In Bash, there are two ways of writing to a file (technically, there are a lot more, but for all intents and purposes for this answer, there are two):

First off is the > operator, as you're using in this line:

echo Course Attendees > list

The > operator will overwrite anything existing in the file with the new contents of the file. In effect, it deletes the file, and creates a new one with the same name.

Secondly is the >> operator, as used here:

echo $name >> list

This will append lines to an existing file, or create a new one if it doesn't exist.

When you run your script, you're always overwriting your course list with the "Course Attendees" header, causing this error. Alter your program to only append lines if the "Course Attendees" header is present. My personal suggestion would be to check if the file exists. If it does, use only the append operation. Otherwise, give it the header and create it.

Or, more elegantly, only run echo Course Attendees > list if the file does not exist. See this SO answer for more info as to how to run a check like this.

Community
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Kaz Wolfe
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  • But want I want is to append a new name as the file has already been created by the shell script, so I should use command to check if the file is there which it will then use "echo" and ">>" command to append the text to the file? – user636667 Dec 30 '16 at 20:51
  • @Mike02x You don't need to do that. If you test for the file not being there, you can add the header. You're already going to append the name, so there's no point in making that a conditional. – Kaz Wolfe Dec 30 '16 at 20:52
  • How can I make it so the script won't end so it would be there for the other users to just type their names and then it would auto append the text into it then? – user636667 Dec 30 '16 at 22:07
  • @Mike02x Look into while loops or similar for Bash. – Kaz Wolfe Dec 30 '16 at 22:27
  • Hey guys, thanks for all your help! I was finally able to make it work after thinking for a very long time! Unfortuantely, I can't add pictures to a comment/reply. @Kaz_Wolfe – user636667 Jan 04 '17 at 20:24