Pass argument to awk inside do loop

I have a large number of tab-separated text files containing a score I’m interested in in the second column:

test_score_1.txt

Title   FRED Chemgauss4 File
24937   -6.111582   A
24972   -7.644171   A
26246   -8.551361   A
21453   -7.291059   A

test_score_2.txt

Title   FRED Chemgauss4 File
14721   -7.322331   B
27280   -6.229842   B
21451   -8.407396   B
10035   -7.482369   B
10037   -7.706176   B

I want to check if I have Titles with a score smaller than a number I define.

The following code defines my score in the script and works:

check_score_1

#!/bin/bash

find . -name 'test_score_*.txt' -type f -print0 |
while read -r -d $'' x; do
    awk '{FS = "t" ; if ($2 < -7.5) print $0}' "$x"
done

If I try to pass an argument to awk like so check_scores_2.sh "-7.5" as shown in check_score_2.sh, that returns all entries from both files.

check_scores_2.sh

#!/bin/bash

find . -name 'test_score_*.txt' -type f -print0 |
while read -r -d $'' x; do
    awk '{FS = "t" ; if ($2 < ARGV[1]) print $0}' "$x"
done

Finally, check_scores_3.sh reveals that I’m actually not passing any arguments from my command line.

check_scores_3.sh

#!/bin/bash

find . -name 'test_score_*.txt' -type f -print0 |
while read -r -d $'' x; do
    awk '{print ARGV[0] "t" ARGV[1] "t" ARGV[2]}' "$x"
done

$ ./check_score_3.sh "-7.5" gives the following output:

awk ./test_score_1.txt  
awk ./test_score_1.txt  
awk ./test_score_1.txt  
awk ./test_score_1.txt  
awk ./test_score_1.txt  
awk ./test_score_2.txt  
awk ./test_score_2.txt  
awk ./test_score_2.txt  
awk ./test_score_2.txt  
awk ./test_score_2.txt  
awk ./test_score_2.txt  

What am I doing wrong?

Answer

In your shell script, the first argument to the shellscript is available as $1. You can assign that value to an awk variable as follows:

find . -name 'test_score_*.txt' -type f -exec awk -v a="$1" -F't' '$2 < a' {} +

Discussion

• Your print0/while read loop is very good. The -exec option offered by find, however, makes it possible to run the same command without any explicit looping.

• The command {if ($2 < -7.5) print $0} can optionally be simplified to just the condition $2 < -7.5. This is because the default action for a condition is print $0.

• Note that the references $1 and $2 are entirely unrelated to each other. Because $1 is in double-quotes, the shell substitutes in for it before the awk command starts to run. The shell interprets $1 to mean the first argument to the script. Because $2 appears in single quotes, the shell leaves it alone and it is interpreted by awk.  Awk interprets it to mean the second field of its current record.