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I am looking to search a file for a column that is 3 letters followed by any 3 or 4 numerals. eg.
if ( $1 ~ /^[A-Z][A-Z][A-Z][0-9][0-9][0-9]/)
However I need the 3 letters to be a variable, so I am looking for the result of SP="ABC" if ( $1 ~ /^/SP/[0-9][0-9][0-9]/)
This however does not work, and I've not found a way to combine a variable and regular expression in the search pattern. Any help greatly appreciated.

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up vote 5 down vote accepted
if ( $1 ~ "^" SP "[0-9]{3}")

You can concatenate strings but not /xxx/s which are in effect more like regular expression matching operators, and with parsing rules that can get confusing (and vary between implementations)

$1 ~ /ABC/ /BCD/

could be seen as the concatenation of $1 matched against the concatenation of /ABC/ (1 or 0 depending on whether $0 matches /ABC/) and /BCD/ (1 or 0 depending on whether $0 matches /BCD/), or $1 matched against /ABC/ (0 or 1) concatenated with $0 matched against /BCD/ which would be confusing enough except that the /regexp/ operator doesn't work well when combined with some others like the concatenation operator here, as there's a possible confusion with the / division operator.

But with parenthesis, you can get interesting (read buggy) behaviours:

$ echo 11 ab | gawk '{print $1 ~ /a/ (/b/)}'
$ echo 11 ab | bwk-awk '{print $1 ~ /a/ (/b/)}'
$ echo b | bwk-awk '{print /a/ - (/b/)}'

(that latter one being the result of /a/ (0) concatenated with the result of - (/b/)).

note that in $1 =~ "^" SP "[0-9]{3}", SP's content is still treated as a regexp (if it's ..., that matches 3 characters, not 3 dots); if that's not wanted:

if (index($1, SP) == 1 && substr($1, length(SP)+1) ~ /^[0-9]{3}/)
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Exactly what I needed. Looks like I had the right idea, just needed quotes instead of slashes. Thank you muchly. – Carlos Jan 27 at 15:11

You can tell awk to read regular expression starting with exact chars, and then with a charater "type" in square brackets, followed by repetition number in curly brackets. Like so:

echo "ABC956" |  awk '{ if( $1 ~ /^ABC[0-9]{3}/) print "HELLOWORLD" }'                                 

You could use logical operator && to test for presence of both variable and the regular expression as well

echo "ABC956" |  awk -v VAR="ABC" '{ if( $1 ~ VAR && $1 ~ /[0-9]{3}/) print "HELLOWORLD" }'            
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Thank you. I had tried this option, but ran into a problem where the data was abcde123, which this captures, but I don't want. – Carlos Jan 27 at 15:14
@Carlos so you want the pattern matching to be case insensitive ? – Serg Jan 27 at 16:17
no, all text in this particular file is upper case. My example of abcde123 was just relative to the extra "de" between abc and 123. – Carlos Jan 28 at 20:24

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