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lecture2

More Terminal

Below, I have listed examples of the many common commands and practices of the shell. If you want to know more about specific commands, you can use man to find out more information.

man find  # will return the man page about find. Press 'q' to get out of this page

Or just do what I did for this entire lesson and search The Google.

Output to Terminal

echo - write arguments to standard output

# Instructions
# echo <text_to_output>

# print user inputted text to standard output
echo 'hello world!'

# OUTPUT:
# hello world!

# enable escaped characters such as new line ('\n')
echo -e 'hello\n world!'

# OUTPUT:
# hello
# world!

cat - print files to standard output

# Instructions
cat <file_to_output>

# output contents of file to standard output
cat myfile.txt

Searching

find - Find a file recursively in a given directory

The find command will search a folder and ALL of its subdirectories. For example, if Judy searches her home folder for a file, find will look in her home folder, her Desktop folder, her cs180 folder, her Projects folder within the cs180 folder … until it has checked every directory and every file for the pattern.

# Instructions
# find <starting directory> <matching criteria and actions>

READ THIS BEFORE YOU USE FIND ON YOUR OWN!!

Never, ever run the FIND command starting at the / directory on the CS machines. This is one of the main rules of the CS Department. Make sure to use find within your home directory.

# allowed
find ~/ -name myfile

# allowed if your current working directory is at or within your home directory
find . -name myfile

# allowed if myfolder is at or within your home directory
find myfolder/ -name myfile

# not allowed because it starts the search at the / directory
# DO NOT EVER RUN THIS!!
find / -name myfile
# DO NOT EVER RUN THIS!!

Actual Examples

# find a file within my Desktop folder or below named lab2key.txt
find ~/Desktop -name "lab2key.txt"

# find all .class files in my cs180/ directory or below and delete them
find ~/cs180 -name "*.class" -exec rm {} \;

# previous command explained
# find <directory to search> -name <name including wildcard> -exec <command to execute> {} \;

# The {}'s are a placeholder for each file that the find command locates
# The \; is the end of the command specified by -exec'

grep - file pattern searcher

grep will search through the CONTENTS of files in order to find a pattern.

Note that this is different from find which will search through file names to match a pattern.

# Instructions
# grep "<search term>" <files_to_search>

# Arguments
# -n : show line number of occurrence
# -i : case-insensitive search
# -w : match whole word  
# -r : search recursively in sub-folders

# search within files of the project5 folder for occurrences of the text "main"
grep -n "main" ~/cs180/project5/*

# search all files in ~/cs180 and its subfolders for the whole word "ShapeFactory"
grep -nrw "ShapeFactory" ~/cs180/

Input/Output Redirection

Standard Input

The standard input is the default input to the system. When you type on the keyboard in a terminal window, you are feeding the standard input stream. When Scanner is used in Java, it takes input from standard input.

# Redirect standard input from user input to a file

# Instructions
# program < file

# Feed the java program with the contents of geo_input.txt
java PlaneGeometry < geo_input.txt

# Send the contents of my_story to the input of grep and search for the term "The End"
grep -n "The End" < my_story

Standard Output

The standard output is the default output of the system, which is usually the terminal window. When characters are sent to the standard output, they show up in a terminal window.

# Redirect standard output from the terminal window to a file

# Instructions
# program > file

# Send the output of the java program to output.txt
java PlaneGeometry > output.txt

# Send the output of the program 'ls' to dir_info
ls > dir_info

# Combine both standard input and standard output redirection
# geo_input.txt will send all text to the scanner
# output will capture all "System.out.print" calls.
java PlaneGeometry < geo_input.txt > output.txt

Pipes

A pipe connects the output of one command to the input of another.

# Instructions
# program1 | program2

# Feed the java program with the contents of geo_input.txt
cat geo_input.txt | java PlaneGeometry

# NOTE: the above command is equivalent to
java PlaneGeometry < geo_input.txt

# search for the term "SCALAR" in the output of PlaneGeometry
cat geo_input.txt | java PlaneGeometry | grep "SCALAR"

Downloading From the Internet

# Instructions
# wget <website>

# Download a file from Kirby's website
wget http://kirbyk.me/secret.html

# Recursively download Kirby's website (download the entire thing)
wget -r http://kirbyk.me

Text Statistics

wc - word, line, character, byte count

# Print the number of lines, words, and characters of file
wc book.txt

# Print the number of lines, words, and characters from standard input
cat book.txt | wc

History

history - command line history

# print recent previous commands
history

# re-enter command number 72
!72  <ENTER>

# print out command number 72 to Standard Output
echo "!72"