Lecture 4 -- Permission & Commands

Text Editor

an application used to create, view and modify text files

Why is a text editor important in linux

many system configuration files are stored as text files and must be edited by administrators

Vim

a powerful command-line text editor with multiple modes (insert and command mode)

Nano

a simple and user-friendly command-line text editor with on-screen shortcuts

Gedit

a GUI-based text editor used in desktop environments, easiest to use

Motion

single-key shortcuts used to navigate within files in command mode (Vim)

Locate

searches for file names using a database (mlocate), very fast but results may be outdated

Find

recursively searches directories using criteria, slower but accurate and real-time

Locate vs Find

• locate uses a database (fast, may be outdated)

• find searches the filesystem directly (slower, accurate)

Which command

displays the full path of a command (e.g. which ls → /bin/ls)

Whereis command

displays locations of binaries, source files and manual pages of a command

cat command

displays and combines text files

head

displays the first 10 lines of a file (default)

tail

displays the last 10 lines of a file (default), use -f to follow updates in real time

less and more

view long files page by page, less is more advanced and preferred

cp command

copies files, use -r option to copy directories recursively

mv command

moves or renames files and directories

touch command

creates an empty file or updates file timestamp

rm

removes files or directories, use -r to remove directories recursively (dangerous)

mkdir

creates directories

rmdir

removes empty directories only

ls

lists directory contents, use -l to display permissions and details

echo

displays text or writes output to a file

tr

translates or replaces characters (e.g. uppercase to lowercase)

wc

counts number of lines, words and characters in a file

sort

sorts lines in a file alphabetically or numerically

cut

extracts specific parts (fields) of text

paste

merges lines of files horizontally

diff

compares two files and shows differences

grep

searches for patterns (text) inside files

awk

a powerful pattern scanning and processing tool for text

sed

a stream editor used to modify text (e.g. search and replace)

ln

creates links between files

Hard link

points to the same data as the original file, remains even if original file is deleted (same inode)

Soft link (symbolic link)

a shortcut to another file, breaks if original file is deleted

text stream

a sequence of text data that can be read or written by commands

standard input (stdin)

input stream used by a command (default: keyboard)

standard output (stdout)

output stream used by a command (default: terminal)

standard error (stderr)

stream used for error messages

tee

displays output and writes it to a file at the same time

/dev/null

a special file that discards all data written to it