Skipping line and regex in awk [duplicate] - regex

Question

This question already has answers here:
how to ignore blank lines and comment lines using awk
(3 answers)
Closed 8 years ago.
I'm working with awk and I need to skip lines that are blank or comments. I've been trying inside the loop to see if it match the regex for this and then using next
{if ($0 ~"/^($|#)/" ) {next;}}
but the if statement is never getting hit and I can't figure out why. (My input has blank lines and comments)
I need to add this line inside of an awkscript in the block, not a command line argument.

Answer 1

Assuming you're inside a block of awk code that doesn't benefit from default print of matching patterns and you need to use an if test , here is the basis for a solution
$ echo "a
b
c
d
#
#e
f
" | awk '{if ($0 ~ /^(#|$)/ ) {next;} ;print}'
produces output of
a
b
c
d
f
If you want to skip blank lines that have spaces/tabs included, you can add
awk '{if ($0 ~ /^(#|[ \t]*$)/ ) {next;} ;print}'
#-------------------^^^^^^
# means char-class of space and tab char
# * means zero or more of preceding
IHTH

Answer 2

In awk, a regular expression is marked by the beginning and ending slashes. If you place it inside quotes, it ceases to be a regex and becomes a string. Thus, replace:
{if ($0 ~"/^($|#)/" ) {next;}}
With:
{if ($0 ~ /^($|#)/ ) {next;}}
Example
Consider the input file:
$ cat input
one
#comment
two
three
four
Now observe the awk script:
$ awk '{if ($0 ~ /^($|#)/ ) {next;}} 1' input
one
two
three
four

Answer 3

You can use the following one:
awk '! /^($|#)/' infile
It uses a default action of print for each line that doesn't begin with # or is a blank one.

Answer 4

awk '/^$|#/{next} {print $0}'
would do the job
or
more simply
awk '/^[^$#]/ '
what it does?
/^[^$#]/ matches each line to the regex and if a match is found, the default action to print the entire record is done.
^ anchors the regex at the begining of the line.
[^$#] negatates the character class. ensures that the start of line is not followed by
$ => line is empty, negation skips the line
# => comment
eg
$ cat input
hello
#world
this is a
test
$ awk '/^[^$#]/ ' input
hello
this is a
test