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Name:

PID: (page 1)

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

if <condition>

then

elif <condition>

then

else

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

for VAR in <sequence>

<commands; $VAR is bound to an element of sequence>

done

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

files=`find written_2`

for file in $files

if [[ -f $file ]] && [[ $file == *Bahamas* ]]

then

wc -l $file

done

bahamas-files.sh

$ ls written_2/

non-fiction travel_guides

$ bash bahamas-files.sh

169 written_2/travel_guides/berlitz2/Bahamas-WhereToGo.txt

24 written_2/travel_guides/berlitz2/Bahamas-Intro.txt

68 written_2/travel_guides/berlitz2/Bahamas-WhatToDo.txt

43 written_2/travel_guides/berlitz2/Bahamas-History.txt

$ javac AgeCalc.java

$ java AgeCalc

1987/6/22

You're 35 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. Which expectation below is incorrect?

AgeCalc.java

check.sh

test-files/

test1.txt "1987/6/22"

test1.txt.expect "You're 35 yrs old."

test2.txt "2024/7/12"

test2.txt.expect "You don't exist yet."

test3.txt "2023/12/1"

test3.txt.expect "You're 0 yrs old."

...

set -e

javac AgeCalc.java

for _____________________________

done

Write a bash script that will run the program on all the test files. Challenge: print an error message if it doesn't match the expectation.

set -e

javac AgeCalc.java

for TEST in test-files/test*.txt

echo Testing `cat $TEST`

result=`java AgeCalc < $TEST`

if [[ $result == `cat $TEST.expect` ]]

then

echo "Success!"

else

echo "Fail, these two strings are not equal:"

echo "Expect:" `cat $TEST.expect`

echo "Actual:" $result

done

import java.util.Scanner;

import java.time.LocalDateTime;

import java.time.temporal.ChronoUnit;

import java.time.Month;

class AgeCalc {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

String s = in.nextLine();

String[] parts = s.split("/");

int year = Integer.parseInt(parts[0]);

Month month = Month.of(Integer.parseInt(parts[1]));

int day = Integer.parseInt(parts[2]);

LocalDateTime now = LocalDateTime.now();

LocalDateTime provided = LocalDateTime.of(year, month, day, 0, 0);

long difference = provided.until(now, ChronoUnit.YEARS);

if(provided.isAfter(now)) { System.out.println("You don't exist yet."); }

else { System.out.println("You're " + difference + " yrs old."); }

}

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Name:

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A process is what our computer keeps track of for each command while it is running. This includes:

Where its standard input comes from (typing or file) and where its standard output should go (terminal or file)
Its memory (like where all the variables and objects are stored) and code (Java bytecode, bash script code)
The command line arguments it started with
Any ports it is listening on, any files it is reading from or writing to.... and lots more!

When a process ends, it has a return code or exit code. The rule is that 0 means success and non-0 means error.

In bash, the exit code of the last process that ran is stored in the special variable: $? (yes, that's a dollar sign then a question mark)

set -e

javac ExitCode.java

java ExitCode 0

echo $?

java ExitCode 1

echo $?

java ExitCode 3

echo $?

class ExitCode {

public static void main(String[] args) {

System.out.println("Exiting with code " + args[0]);

System.exit(Integer.parseInt(args[0]));

}

run-exit-code.sh

ExitCode.java

bash-3.2$ bash run-exit-code.sh

# what's the output? why?

bash-3.2$ ls does-not-exist.txt

ls: does-not-exist: No such file or directory

bash-3.2$ echo $? # fill in a guess/the result below

_________________________________

bash-3.2$ cat BadFile.java

class Bad {

private statik void mane(Strong[] orgs) {}

}

bash-3.2$ javac BadFile.java

BadFile.java:2: error: <identifier> expected

private statik void mane(Strong[] orgs) {}

1 error

bash-3.2$ echo $?

bash-3.2$ echo $? # fill in a guess/the result below

________________________________

bash-3.2$ cat GoodFile.java

class Main {

public static void main(String[] args) { }

}

bash-3.2$ javac GoodFile.java

bash-3.2$ echo $? $ fill in a guess/the result below

________________________________

Where might it be useful to use or check an exit code?

What happens when you submit a PA in CSE12?