Basic UNIX commands

Know more about a cmd use $man command

Directory

• pwd

Show your Present Working Directory

• mkdir

Make a directory

• cd dirname

Change directory

• cd

Return to your home directory

• cd ..

Return to the upper directory

• cd /

Return to the root directory

Finding things

• ls | grep extension

Will show you all files with the 'extension'

e.g., 

• ll | grep string

Will show you all files with the 'string'

e.g.,  

• grep string filename(s)/grep [options] pattern [files]

Looks for the string in the files (txt file typically).

e.g., 

$grep python grep_example.txt

txt file (cat grep_example.txt)

Result:

More options

-c : This prints only a count of the lines that match a pattern

-h : Display the matched lines, but do not display the filenames.

-i : Ignores, case for matching

-l : Displays list of filenames only.

-n : Display the matched lines and their line numbers.

-v : This prints out all the lines that do not matches the pattern

-e exp : Specifies expression with this option. Can use multiple times.

-f file : Takes patterns from file, one per line.

-E : Treats pattern as an extended regular expression (ERE)

-w : Match whole word

-o : Print only the matched parts of a matching line,

 with each such part on a separate output line.

-A n : Prints searched line and nlines after the result.

-B n : Prints searched line and n line before the result.

-C n : Prints searched line and n lines after before the result.

Examples,

File

• ls

Lists your files

• ls -l

lists your files in 'long format', which contains lots of useful information, e.g. the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified.

• ls -a

lists all files, including the ones whose filenames begin in a dot, which you do not always want to see.
There are many more options, for example to list files by size, by date, recursively etc.

• touch filename

Create a new file

e.g., $touch grep_example.txt

• rm filename

Delete a file

• rm -r dir (rmdir dir)

Delete a directory

• cp filename1 filename2

Copies a file

• more filename

Shows the first part of a file, just as much as will fit on one screen

Just hit the space bar to see more or q to quit. You can use /pattern to search for a pattern.

More examples https://shapeshed.com/unix-more/

• chmod options filename 

Lets you change the read, write, and execute permissions on your files. 

The default is that only you can look at them and change them, but you may sometimes want to change these permissions. 

For example, chmod o+r filename will make the file readable for everyone, 

and chmod o-r filename will make it unreadable for others again. 

Note that for someone to be able to actually look at the file the directories it is in need to be at least executable.

More https://www.geeksforgeeks.org/chmod-command-linux/

Other

• export variable=value (now space before and after =)

$export mytestpath = test123

• echo $variable

Shows the value of an environment variable

$echo $mytestpath

>>test123

• clear

cleans screen

• source filename

You need to source your dotfiles after making changes for them to take effect (or log off and in again)

More Unix commands

https://mally.stanford.edu/~sr/computing/more-unix.html

https://mally.stanford.edu/~sr/computing/basic-unix.html