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Table of Contents
UNIX 102
Required Reading
Modifying Program Behavior
Many commands will run without any additional information from the user, but most options will also allow you to modify it's behavior by passing it new information. Obviously one method of passing information from the user to a program is for the program to print a question to the screen and wait for the user to respond. However, that's not a very efficient method of interaction if you're trying to automate your workflow. A better method would be for the user to give the program access to everything it needs to know up front so that the computer doesn't have to stop and ask questions. This also allows long programs or scripts to run overnight while the user goes home, which is very important for users who, for instance, want to process large amounts of data or run large numbers of simulations.
Options and Arguments
One method of passing extra information to a program is to add this information to the command line when you type your command into the shell. The command line is the entire string of characters that you type into the shell, starting with the first character and ending when you press return.
Command line options for a program can usually be found by either typing the command, then a space, and then typing
-h
or
--help
. Most programs will respond by giving you additional information about options and arguments that can be passed to the command on the command line. Another way is to type
man <command>
to see if the program comes with it's own documentation.
Most command line options in Unix are prefixed by a single or double dash (- or –). (Note: The difference between single and double dashes can be difficult to see on this web page. I'll let you know if something is single or double.)
Examples of command line arguments:
peek@catus:~/Documents/LinuxTutorial$ ls Aware_-_Kontinuum.flac log-messages.txt README Glaciers-SD.mp4 MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv
In the above example, I type the command
ls
without any arguments. The output is ls' default behavior. But I can modify what ls does:
peek@catus:~/Documents/LinuxTutorial$ ls -1 Aware_-_Kontinuum.flac Glaciers-SD.mp4 log-messages.txt MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv README
This time I pass ls -1, telling it that I want it to print everything in only one column. This is especially handy for piping the output of ls to another command or script that will do something useful.
peek@catus:~/Documents/LinuxTutorial$ ls -al total 35620 drwxrwx--- 2 peek peek 4096 May 13 13:33 . drwxr-x--- 47 peek peek 4096 May 13 12:03 .. -rw-rw---- 1 peek peek 30725004 May 12 15:32 Aware_-_Kontinuum.flac -rw-rw---- 1 peek peek 2358156 May 12 15:29 Glaciers-SD.mp4 -rw-r----- 1 peek peek 3359600 May 12 16:02 log-messages.txt -rw-rw---- 1 peek peek 3188 May 12 16:12 MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv -rw-rw---- 1 peek peek 579 May 12 15:41 README peek@catus:~/Documents/LinuxTutorial$
The above shows an argument that will tell ls to show me a lot of extra information about the files in this directory. Specifically, column one shows me permissions, columns 3 and 4 show me user and group ownership, column 5 shows me file size in bytes, and columns 6-8 shows me the date and time that the file or directory was last modified.
Configuration Files
Another method of passing information along to a program is by creating or editing a configuration file. Configuration files are specific to the program that reads them, so specifics won't be given here. Just being aware of their existence can make your life easier.
Environment Variables
A third common method of passing information to a program is through environment variables. These are special variables that are given to the shell and the shell will remember them and pass their values along to any scripts or programs that the shell executes.
Some Useful Commands
| Command | Description |
|---|---|
pwd | Returns the shell's current working directory. $ pwd /home/peek |
cd | Used by itself, the cd command will return the user's current working directory to the top of their home area (usually /home/<username>). When used with a command line argument, the cd command will attempt to change the current working directory to the directory name passed to it as an argument. $ pwd /home/peek/usr/bin $ cd $ pwd /home/peek $ cd /tmp $ pwd /tmp |
ls | Used by itself, the ls command will list the directory contents of the current working directory. The output format can be modified with command line arguments – and, optionally, the user may give a list of files or directories to list. $ ls Aware_-_Kontinuum.flac log-messages.txt README Glaciers-SD.mp4 MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv $ ls -al total 35620 drwxrwx--- 2 peek peek 4096 May 13 13:33 . drwxr-x--- 47 peek peek 4096 May 13 12:03 .. -rw-rw---- 1 peek peek 30725004 May 12 15:32 Aware_-_Kontinuum.flac -rw-rw---- 1 peek peek 2358156 May 12 15:29 Glaciers-SD.mp4 -rw-r----- 1 peek peek 3359600 May 12 16:02 log-messages.txt -rw-rw---- 1 peek peek 3188 May 12 16:12 MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv -rw-rw---- 1 peek peek 579 May 12 15:41 README $ ls /tmp aws_root.log dvdcss-DnlBhJ dvdcss-q9Iio2 hsperfdata_root ssh-8eL6NRDqQg ssh-gUTLY6GtJG systemd-private-6289425d307e43a98f4f52405e0d97ac-colord.service-IaXZv6 systemd-private-6289425d307e43a98f4f52405e0d97ac-tor@default.service-CIBSIM $ ls /tmp /var/tmp /tmp: aws_root.log dvdcss-DnlBhJ dvdcss-q9Iio2 hsperfdata_root ssh-8eL6NRDqQg ssh-gUTLY6GtJG systemd-private-6289425d307e43a98f4f52405e0d97ac-colord.service-IaXZv6 systemd-private-6289425d307e43a98f4f52405e0d97ac-tor@default.service-CIBSIM /var/tmp: systemd-private-6008fcbada2e41ed9bddfe6b012eb599-colord.service-c0jtLz systemd-private-6008fcbada2e41ed9bddfe6b012eb599-tor@default.service-B7IV7c systemd-private-6289425d307e43a98f4f52405e0d97ac-colord.service-iHELip systemd-private-6289425d307e43a98f4f52405e0d97ac-tor@default.service-J0PeqU |
file | Tells you what type of data is in a file. $ ls -1 Aware_-_Kontinuum.flac Glaciers-SD.mp4 log-messages.txt MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv README $ file README README: ASCII text $ file --mime-type * Aware_-_Kontinuum.flac: audio/x-flac Glaciers-SD.mp4: video/mp4 log-messages.txt: text/plain MendelMax_3_Full_Kit_Packing_Slip_-_Sheet1.csv: text/plain README: text/plain |
less | Lets you view a file's contents. If the file's contents are longer than a single page on your terminal, then less will pause and wait for you to press the space bar before it continues with the next page. Less will also allow you to perform searches $ less README
This is a standard README file. It's a plain text file that tells you
something about the contents of the other files and directories located here.
Readme files aren't always available but it's nice when they are.
Attribution:
* Glaciers-SD.mp4
Science World: How do you protect glaciers?
Released by: Polyester Studio
Date: April 28, 2016 (approx.)
URL: https://vimeo.com/164133990
* Aware_-_Kontinuum.flac
Kontinuum - Aware [NCS Release]
Released by: NoCopyrightSounds
Date: May 27, 2015
URL: https://soundcloud.com/nocopyrightsounds/kontinuum-aware-ncs-release
~
~
~
~
README (END)
|
mkdir rmdir | Create or remove a directory. $ ls -ald ERASEME ls: cannot access 'ERASEME': No such file or directory $ mkdir ERASEME $ ls -ald ERASEME drwxrwx--- 2 peek peek 4096 May 16 14:04 ERASEME $ rmdir ERASEME $ ls -ald ERASEME ls: cannot access 'ERASEME': No such file or directory |
cp | Copy a file to a new filename, or to a new directory. $ mkdir ERASME $ ls -ald ERASEME/* ls: cannot access 'ERASEME/*': No such file or directory $ cp README ERASEME/ $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/README $ cp README ERASEME/mullets-are-a-way-of-life $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:16 ERASEME/mullets-are-a-way-of-life -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/README |
rm | Remove a file (NOTE: THERE IS NO GOING BACK!) $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:16 ERASEME/mullets-are-a-way-of-life -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/README $ rm ERASEME/mullets-are-a-way-of-life $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/README |
mv | Move or rename a file. $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/README $ mv ERASEME/README ERASEME/duck-duck-goose $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/duck-duck-goose $ mkdir ERASEME/subdirectory $ ls -ald ERASEME/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/duck-duck-goose drwxrwx--- 2 peek peek 4096 May 16 14:24 ERASEME/subdirectory $ mv ERASEME/duck-duck-goose ERASEME/subdirectory $ ls -ald ERASEME/* drwxrwx--- 2 peek peek 4096 May 16 14:25 ERASEME/subdirectory $ ls -ald ERASEME/subdirectory/* -rw-rw---- 1 peek peek 579 May 16 14:15 ERASEME/subdirectory/duck-duck-goose |
find | Locates a file or directory somewhere inside either the current directory or a subdirectory. Find is a very powerful tool, and I won't cover it's use in depth here, but I introduce it so that you know what I'm talking about when I use it later. When run without any command line arguments, find will print out a recursive listing of all files and directories located in the current directory and below. That's good enough for now. |
cat | Copies input to output. |
wc | Counts characters, words, and lines. |
head -<n> | Prints the first <n> lines of input, then ignores the rest. |
tail -<n> | Prints the last <n> lines of input, then ignores the rest. |
Playing Around
Now that you have a few commands to play with, let's play with them:
| Type: | $ mkdir /tmp/playground |
|---|---|
| Type: | $ find /tmp/playground /tmp/playground</code | ^ Type: | <code>$ cd /tmp/playground |
| Type: | pwd /tmp/playground |
| Type: | $ mkdir dir1 dir2 |
| Type: | $ cp /etc/passwd . |
| Type: | $ find . ./passwd ./dir1 ./dir2 |
| Type: | mv passwd fun |
| Type: | $ find . ./dir1 ./dir2 ./fun |
| Type: | mv fun dir1 |
| Type: | $ find . ./dir1 ./dir1/fun ./dir2 |
| Type: | mv dir1 dir2 |
| Type: | $ find . ./dir2 ./dir2/dir1 ./dir2/dir1/fun |
| Type: | cd |
| Type: | rmdir /tmp/playground rmdir: failed to remove '/tmp/playground': Directory not empty |
| Type: | rm /tmp/playground/dir2/dir1/fun |
| Type: | find /tmp/playground /tmp/playground /tmp/playground/dir2 /tmp/playground/dir2/dir1 |
| Type: | rmdir /tmp/playground/dir2/dir1 |
| Type: | rmdir /tmp/playground/dir2 |
| Type: | rmdir /tmp/playground |
