Sstrhsrtj

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.