Ygtjki

Having the following in one of my shell functions:

function _process () 
 awk -v l="$line" '
 BEGIN p=0
 /'"$1"'/ p=1
 END if(p) print l >> "outfile.txt" 
 '

, so when called as _process $arg, $arg gets passed as $1, and used as a search pattern. It works this way, because shell expands $1 in place of awk pattern! Also l can be used inside awk program, being declared with -v l="$line". All fine.

Is it possible in same manner give pattern to search as a variable?

Following will not work,

awk -v l="$line" -v search="$pattern" '
 BEGIN p=0
 /search/ p=1
 END if(p) print l >> "outfile.txt" 
 '

,as awk will not interpret /search/ as a variable, but instead literally.

Use awk's ~ operator, and you don't need to provide a literal regex on the right-hand side:

function _process () 
 awk -v l="$line" -v pattern="$1" '
 $0 ~ pattern p=1 
 END if(p) print l >> "outfile.txt"
 ' 

Although this would be more efficient (don't have to read the whole file)

function _process () 
 grep -q "$1" && echo "$line"

Depending on the pattern, may want grep -Eq "$1"

awk -v pattern="$1" '$0 ~ pattern'

Has an issue in that awk expands the ANSI C escape sequences (like n for newline, f for form feed, \ for backslash and so on) in $1. So it becomes an issue if $1 contains backslash characters which is common in regular expressions. Another approach that doesn't suffer from that issue is to write it:

PATTERN=$1 awk '$0 ~ ENVIRON["PATTERN"]'

How bad it's going to be will depend on the awk implementation.

$ nawk -v 'a=.' 'BEGIN print a'
.
$ mawk -v 'a=.' 'BEGIN print a'
.
$ gawk -v 'a=.' 'BEGIN print a'
gawk: warning: escape sequence `.' treated as plain `.'
.

All awks work the same for valid escape sequences though:

$ a='\-b' awk 'BEGIN print ENVIRON["a"]' | od -tc
0000000 - b n
0000006

(content of $a passed as-is)

$ awk -v a='\-b' 'BEGIN print a' | od -tc
0000000 - b n
0000004

(\ changed to and b changed to a backspace character).

Try something like:

awk -v l="$line" -v search="$pattern" 'BEGIN p=0; if ( match( $0, search )) p=1; END if(p) print l >> "outfile.txt" '

No, but you can simply interpolate the pattern into the double-quoted string you pass to awk:

awk -v l="$line" "BEGIN p=0; /$pattern/ p=1; END if(p) print l >> "outfile.txt" "

Note that you now have to escape the double-quoted awk literal, but it is still the simplest way of accomplishing this.

You could use the eval function which resolves in this example the nets variable before the awk is run.

nets="searchtext"
eval "awk '/"$nets"/'" file.txt