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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);

}

}

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$ java Read

What's your name? JoeTyped

Hello JoeTyped

$ cat name.txt

JoeFromFile

$ java Read < name.txt

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Read.java

«command» < «file» Input redirection – use contents of «file» as the standard input to the command. That's what you would type!

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bash has for statements! They can iterate over many things, including lists of paths or lines of output.

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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

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javac AgeCalc.java

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for _____________________________

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done

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Let’s write a bash script that will run the program on all the test files.

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bash has if statements! elif/else are optional, and there can be multiple elif clauses.

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if <condition>

then

<commands>

elif <condition>

then

<commands>

else

<commands>

fi

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Bash has variables, which are declared with

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NAME=value

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Bash also lets you store the output of a program in a variable, with:

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NAME=$(some-command with some argos)

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Bash also lets you store the output of a program in a file, with:

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command > file

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This last example is called output redirection.

Some common <condition>s (iff means "if and only if"):

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[[ -e <val> ]] – true iff the path val exists

[[ -f <val> ]] – true iff the path val exists and is a file

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[[ ______ <val> ]] – true iff the path val exists and is a directory

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[[ <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>

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[[ <val1> ______ <val2> ]] – true iff <val1> is less than <val2>

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[[ <val1> == <pattern> ]] – true iff val1 matches the pattern

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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.

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A <pattern> here could be a constant string, or something using * like *Bahamas*.

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set -e

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javac AgeCalc.java

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for _____________________________

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done

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Let’s update the AgeCalc script to print out whether each test matched its expectation

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Example directory structure, file contents in parentheses

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some-files/

|- a.txt ("hello\n")

|- more-files/

|- b.txt ("hi\n")

|- c.java ("psvm\n")

|- even-more-files/

|- d.java ("junit\ntest")

|- a.txt ("nested file\n")

find «path»: Recursively traverse the given path and list all files in that directory and subdirectories

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wc «file»: Print the number of lines, words, and characters in a file or files

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grep «string» «files»: Search a file or files for the given string, print matching lines

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«command» > «file» Save the output of the command in the given file. Overwrites the file!

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* (asterisk, star) Used to create patterns, which can refer to multiple files.�Examples: lib/*.jar, *.txt

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echo «arguments» Print the arguments to the terminal

$ ls some-files/*

$ find some-files

some-files

some-files/even-more-files

some-files/even-more-files/d.java

some-files/even-more-files/a.txt

some-files/more-files

some-files/more-files/c.java

some-files/more-files/b.txt

some-files/a.txt

Which command or commands (do you think) produces the output on the right, and why? Make a guess!

$ wc some-files/a.txt

$ wc some-files/even-more-files/a.txt

1 2 12 Joe hid a little bit of output here

$ grep "e" some-files/a.txt

$ grep "e" some-files/even-more-files/a.txt

hello

$ grep "e" */a.txt

$ grep "e" */*/a.txt */a.txt

$ grep "e" */*/a.txt

some-files/even-more-files/a.txt:nested

some-files/a.txt:hello

$ find some-files > files.txt

$ grep ".txt" some-files

$ find some-files > files.txt

$ grep ".txt" files.txt

some-files/even-more-files/a.txt

some-files/more-files/b.txt

some-files/a.txt