welcome to the video tutorial on regular
expressions in Linux so what are regular
expressions well they are special
characters no not these yes
which help search data and match complex
patterns regular expressions are
shortened as reg exp or res X some of
the commonly used commands with regular
expressions are TR sed VI and gr e P
these are some of the basic projects let
us learn their practical use let's
consider this sample file now we will
use the GRE P command to look for lines
containing the letter A let's use a
regular expression now using the cat
symbol we will search for the content
that starts with the character a the
caret matches the start of a string this
is why only lines that start with the
character a are filtered lines which do
not contain the character a at the start
arek note let us look into another
example here we will look for the
character T in the same file sample now
let us select only those lines which end
with the character T for this we will
need to use this regular expression
which matches the end of the strength
this is how we can use regular
expressions moving on to the interval
regular expressions they tell us about
the number of occurrences of a character
or string they are
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so if we use the first expression it
will match the preceding character
appearing and times exactly let us write
on terminal let us filter out all the
lines that contain the character P now
if we want to check the character P
appearing exactly two times in a string
one after the other for this the syntax
would be which will give us this result
it should be noted here that you need to
add - capital e with these regular
expressions the next is the extended
regular expressions these contain
combinations of more than one
expressions some of them are so if we
use the backward slash with a plus sign
it will match one or more occurrence of
the previous character let us learn
there practical use here we have
searched for the character T suppose we
want to filter out lines where character
a precedes character T we would have to
use the command like sense
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running this command would give us this
result this is how we can use the
extended regular expressions
the syntax for base expansion is either
a sequence or a comma separated list of
items inside curly braces the starting
and end of items in a sequence are
separated by two periods let us go
through some of the examples here we
would use the echo command to create
strings using the brace expansion
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another example of the same would be
this would create a strength from A to Z
one more example would be this
an advanced example of the brace
expansion is this
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this is how we can create strength using
the base expansion to recap what we have
learned reading expressions are a set of
characters used to check patterns and
strengths they're also called read exp
and regex
it is important to learn regular
expressions for writing scripts some
basic regular expressions are the period
symbol replaces any character the caret
matches the start of a strain the dollar
sign matches the end of earth strength
some extended regular expressions are
here the backslash used with the plus
sign matches one or more occurrence of
the previous character the backslash
used with a question mark matches zero
or one occurrence of the previous
character some interval regular
expressions are here the N in the curly
braces matches the preceding character
appearing n times exactly in the second
expression the N and M and the curly
braces match preceding character
appearing n times but not more than m
and the last total expression displayed
here matches the preceding character
only when it appears and times or more
the brace expansion is used to generate
strings it helps in creating multiple
strings out of one thanks for watching
this tutorial I hope to see you in the
next one