Text Files Manipulation

stdin

main input stream, <

output stream - default display monitor, >

error stream - default display monitor, 2>

| send out of one to in of another, tee does'nt capture the stream, duplicates it

get the env variable list

simple tool, splits the output according to the given delimeter or according to the postion of the letter

similar to cat but for lines, you can concatenate every line and give a delimeter to seperate them

see the starting lines of a file, you can provide the no of lines you wanted to see

see the ending lines of a file, you can provide the number of lines you wanted to see

replace tabs with spaces, and spaces with tabs

join and spilit files based on some common column

sort a file, can be in reverse or in numerical order

translate a set of characters into another characters, like uppercase to lowercase

removes duplicate form files

count the number of words, character and lines in a file

find some words in the file, use of regex is also availiable

perl based command to extract text
sed 's/this/that/g - s means substitute, this with that
sed -i 's/this/that/g - s means substitute, this with that, -i means inplace, so if you provide a file it will change that

Simple regular expressions (also called basic regular expressions or BREs)
are the most basic form of regular expressions.
They are supported by most grep implementations and use a minimal set of characters and metacharacters.
Some examples of simple regular expressions include abc, [0-9], and ^a.*z$.
Extended regular expressions (also called EREs)
are a slightly more powerful version of regular expressions.
They add several additional metacharacters and allow the use of some backslashes as escape characters.
Extended regular expressions are supported by grep with the -E option and by sed with the -r option.
Some examples of extended regular expressions include (abc|def), \d, and ^a.*?z$.
Perl-compatible regular expressions (also called PCREs)
are a more powerful version of regular expressions that are used by the Perl programming language.
They support most of the features of EREs, as well as several additional features such as backreferences, lookaheads, and nested character classes.
PCREs are supported by the pcregrep and pcre2grep commands, as well as by many programming languages and text processing tools.
Some examples of PCREs include (?<word>\w+), (?<=abc)def, and ^a(?>.*)z$.

There are many other versions of regular expressions but every tool support atleast on of these.