Text editors, and processing text streams through filters

Here’s a complete and structured guide for:

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📝 Text Editors, Text Streams, Filters, and Redirection

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1. 🔤 Vi vs Vim

Feature	vi	vim (Vi IMproved)
Availability	Always installed	May require install (sudo apt install vim)
Features	Basic editing	Syntax highlighting, undo, plugins, multi-level undo
Usage	Lightweight	Powerful and extensible

Basic vi / vim Usage:

Command	Action
i	Insert mode
Esc	Exit to command mode
:w	Save
:q	Quit
:wq or ZZ	Save and quit
:q!	Quit without saving
dd	Delete line
yy	Yank (copy) line
p	Paste line

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2. 🔁 Output Redirection & GNU Text Utilities

Tool	Example	Description
cat	cat file.txt	Print file contents
cut	cut -d: -f1 /etc/passwd	Cut fields by delimiter
sort	sort file.txt	Sort lines
uniq	`sort file.txt | uniq`	Remove duplicates
expand	expand file.txt	Convert tabs to spaces
join	join file1 file2	Join files by common field
split	split -l 100 file	Split into chunks
wc	wc -l file.txt	Line/word/char count
sed	sed 's/foo/bar/' file	Stream edit
head / tail	head -n 10 file	Show first/last N lines

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3. 🔗 Streams, Pipes, and Redirects

Symbol	Description
>	Redirect output to file (overwrite)
>>	Redirect output to file (append)
<	Redirect file to command input
` | `	Pipe: output → input of another
tee	Output to screen and file: `cmd | tee file.txt`
xargs	Pass input as command arguments: `cat list.txt | xargs rm`

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4. 🔍 Search with Regular Expressions

Tool	Description	Example
grep	Basic search	grep "error" logfile
egrep	Extended regex (same as grep -E)	`egrep “foo | bar” file`
fgrep	Fixed string search (no regex)	fgrep "text" file
sed	Search and replace	sed 's/old/new/g' file.txt
Regex examples
.	Any character
*	Zero or more
^	Line start
$	Line end
[abc]	Match a, b, or c
[^abc]	Not a, b, or c
\d	Digit (in grep -P)

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