Name:
PID: (page 1)
import java.util.Scanner;
class Read {
public static void main(String[] args) {
System.out.print("What's your name? ");
Scanner in;
in = new Scanner(System.in);
String s = in.nextLine();
System.out.println("Hello " + s);
}
}
$ java Read
What's your name? JoeTyped
Hello JoeTyped
$ cat name.txt
JoeFromFile
$ java Read < name.txt
Read.java
«command» < «file» Input redirection – use contents of «file» as the standard input to the command. That's what you would type!
bash has for statements! They can iterate over many things, including lists of paths or lines of output.
for VAR in <sequence>
do
<commands; $VAR is bound to an element of sequence>
done
$ javac AgeCalc.java
$ java AgeCalc
1987/6/22
You're 36 yrs old.
$ java AgeCalc
2024/7/12
You don't exist yet.
Assume we have a program with the following behavior.
Underlined text is typed at standard input
Assume we have a directory of files like below, where the contents of each file is in quotes next to it.
AgeCalc.java
check.sh
test-files/
test1.txt "1987/6/22"
test1.txt.expect "You're 36 yrs old."
test2.txt "2024/7/12"
test2.txt.expect "You don't exist yet."
test3.txt "2023/12/5"
test3.txt.expect "You're 0 yrs old."
...
set -e
javac AgeCalc.java
for _____________________________
done
Let’s write a bash script that will run the program on all the test files.
Name:
PID: (page 2)
bash has if statements! elif/else are optional, and there can be multiple elif clauses.
if <condition>
then
<commands>
elif <condition>
then
<commands>
else
<commands>
fi
Bash has variables, which are declared with
NAME=value
Bash also lets you store the output of a program in a variable, with:
NAME=$(some-command with some argos)
Bash also lets you store the output of a program in a file, with:
command > file
This last example is called output redirection.
Some common <condition>s (iff means "if and only if"):
[[ -e <val> ]] – true iff the path val exists
[[ -f <val> ]] – true iff the path val exists and is a file
[[ ______ <val> ]] – true iff the path val exists and is a directory
[[ <val1> -eq <val2> ]] – true iff values arithmetically equal
[[ <val1> -ne <val2> ]] – false iff values arithmetically equal
[[ <val1> -gt <val2> ]] – true iff <val1> is greater than <val2>
[[ <val1> ______ <val2> ]] – true iff <val1> is less than <val2>
[[ <val1> == <pattern> ]] – true iff val1 matches the pattern
A <val> here could be a use of a bash variable (like $SOMEVAR), or constant string values like "0" or "1", or a written out path like data-dir/. Generally think of these all as being string values.
A <pattern> here could be a constant string, or something using * like *Bahamas*.
set -e
javac AgeCalc.java
for _____________________________
done
Let’s update the AgeCalc script to print out whether each test matched its expectation