match variable string at end of field with awk - regex

Question

Yet again my unfamiliarity with AWK lets me down, I can't figure out how to match a variable at the end of a line?
This would be fairly trivial with grep etc, but I'm interested in matching integers at the end of a string in a specific field of a tsv, and all the posts suggest (and I believe it to be the case!) that awk is the way to go.
If I want to just match a single one explicity, that's easy:
Here's my example file:
PVClopT_11 PAU_02102 PAU_02064 1pqx 1pqx_A 37.4 13 0.00035 31.4 >1pqx_A Conserved hypothetical protein; ZR18,structure, autostructure,spins,autoassign, northeast structural genomics consortium; NMR {Staphylococcus aureus subsp} SCOP: d.267.1.1 PDB: 2ffm_A 2m6q_A 2m8w_A No DOI found.
PVCpnf_18 PAK_3526 PAK_03186 3fxq 3fxq_A 99.7 2.7e-21 7e-26 122.2 >3fxq_A LYSR type regulator of TSAMBCD; transcriptional regulator, LTTR, TSAR, WHTH, DNA- transcription, transcription regulation; 1.85A {Comamonas testosteroni} PDB: 3fxr_A* 3fxu_A* 3fzj_A 3n6t_A 3n6u_A* 10.1111/j.1365-2958.2010.07043.x
PVCunit1_19 PAU_02807 PAU_02793 3kx6 3kx6_A 19.7 45 0.0012 31.3 >3kx6_A Fructose-bisphosphate aldolase; ssgcid, NIH, niaid, SBRI, UW, emerald biostructures, glycolysis, lyase, STRU genomics; HET: CIT; 2.10A {Babesia bovis} No DOI found.
PVClumt_17 PAU_02231 PAU_02190 3lfh 3lfh_A 39.7 12 0.0003 28.9 >3lfh_A Manxa, phosphotransferase system, mannose/fructose-speci component IIA; PTS; 1.80A {Thermoanaerobacter tengcongensis} No DOI found.
PVCcif_11 plu2521 PLT_02558 3h2t 3h2t_A 96.6 2.6e-05 6.7e-10 79.0 >3h2t_A Baseplate structural protein GP6; viral protein, virion; 3.20A {Enterobacteria phage T4} PDB: 3h3w_A 3h3y_A 10.1016/j.str.2009.04.005
PVCpnf_16 PAU_03338 PAU_03377 5jbr 5jbr_A 29.2 22 0.00058 23.9 >5jbr_A Uncharacterized protein BCAV_2135; structural genomics, PSI-biology, midwest center for structu genomics, MCSG, unknown function; 1.65A {Beutenbergia cavernae} No DOI found.
PVCunit1_17 PAK_2892 PAK_02622 1cii 1cii_A 63.2 2.7 6.9e-05 41.7 >1cii_A Colicin IA; bacteriocin, ION channel formation, transmembrane protein; 3.00A {Escherichia coli} SCOP: f.1.1.1 h.4.3.1 10.1038/385461a0
PVCunit1_11 PAK_2886 PAK_02616 3h2t 3h2t_A 96.6 1.9e-05 4.9e-10 79.9 >3h2t_A Baseplate structural protein GP6; viral protein, virion; 3.20A {Enterobacteria phage T4} PDB: 3h3w_A 3h3y_A 10.1016/j.str.2009.04.005
PVCpnf_11 PAU_03343 PAU_03382 3h2t 3h2t_A 97.4 4.4e-07 1.2e-11 89.7 >3h2t_A Baseplate structural protein GP6; viral protein, virion; 3.20A {Enterobacteria phage T4} PDB: 3h3w_A 3h3y_A 10.1016/j.str.2009.04.005
PVCunit1_5 afp5 PAU_02779 4tv4 4tv4_A 63.6 2.6 6.7e-05 30.5 >4tv4_A Uncharacterized protein; unknown function, ssgcid, virulence, structural genomics; 2.10A {Burkholderia pseudomallei} No DOI found.
And I can pull out all the lines which have a "_11" at the end of the first column by running the following on the commandline:
awk '{ if ($1 ~ /_11$/) { print } }' 02052017_HHresults_sorted.tsv
I want to enclose this in a loop to cover all integers from 1 - 5 (for instance), but I'm having trouble passing a variable in to the text match.
I expect it should be something like the following, but $i$ seems like its probably incorrect and by google-fu failed me:
awk 'BEGIN{ for (i=1;i<=5;i++){ if ($1 ~ /_$i$/) { print } } }' 02052017_HHresults_sorted.tsv
There may be other issues I haven't spotted with that awk command too, as I say, I'm not very awk-savvy.
EDIT FOR CLARIFICATION
I want to separate out all the matches, so can't use a character class. i.e. I want all the lines ending in "_1" in one file, then all the ones ending in "_2" in another, and so on (hence the loop).

Answer 1

You can't put variables inside //. Use string concatenation, which is done by simply putting the strings adjacent to each other in awk. You don't need to use a regexp literal when you use the ~ operator, it always treats the second argument as a regexp.
awk '{ for (i = 1; i <= 5; i++) {
if ( $1 ~ ("_" i "$") ) { print; break; }
}' 02052017_HHresults_sorted.tsv

Answer 2

It sounds like you're thinking about this all wrong and what you really need is just (with GNU awk for gensub()):
awk '{ print > ("out" gensub(/.*_/,"",1,$1)) }' 02052017_HHresults_sorted.tsv
or with any awk:
awk '{ n=$1; sub(/.*_/,"",n); print > ("out" n) }' 02052017_HHresults_sorted.tsv

Answer 3

No need to loop, use regex character class [..]:
awk 'match($1,/_([1-5])$/,a){ print >> a[1]".txt" }' 02052017_HHresults_sorted.tsv