将bash数组元素传递给awk regex内部循环

Question

I'm trying to search through a file using awk, by looping over elements of a bash array. This is what I'm currently doing

myarray[1] = 441
myarray[2] = 123

for i in "${myarray[@]}"
do
awk '{if ($4 == '"$i"') print $0}' myfile.txt > newfile.txt
done

Is it possible to access elements of a bash array in awk in this way?

Answer 1

This is not the right way to pass a shell variable (or BASH array element) to awk. Use it with -v option:

myarray=(441 123)

for i in "${myarray[@]}'"; do
   awk -v i="$i" '$4 == i' myfile.txt > newfile.txt
done

• -vi="$i" makes shell variable $i available inside awk as an awk variable i
• $4 == i is equivalent of {if ($4 == i) print $0} since print $0 is the default action

Answer 2

There's no need for a bash loop; you can do the whole thing in awk:

my_array=(441 123)
awk -varr="${my_array[*]}" 'BEGIN{split(arr,a); for(i in a)b[a[i]]} $4 in b' file

The contents of the shell array are passed to awk as a single string, with a space in between each element. split is used to create an awk array from the string. Array a looks like this:

a[1]=441; a[2]=123

The for loop creates an array b with two keys, b[441] and b[123] .

Lines are printed when the 4th column matches one of the array keys.

Bear in mind that this approach fails when the elements in the array contain spaces.

Answer 3

You can avoid looping through the bash array elements externally. In the following, the array elements are passed at one shot to awk and accessed within awk using ARGV . Also, there's no reason why awk cannot write to the output file directly

awk -v len="${#myarray[@]}" '
BEGIN{t=ARGC; ARGC-=len; for(i=2; i<t; ++i) b[ARGV[i]]++ };
$4 in b { print > "newfile.txt"}' myfile.txt  "${myarray[@]}"

Answer 4

you can also construct an awk regex:

myarray=(441 123)
regex=$(IFS=\|;echo "^(${myarray[*]})\$")
awk -v regex="$regex" '$4 ~ regex' myfile.txt > newfile.txt

However, do be careful if there are metacharacters (ie '*', '\\', '?' etc) in any element of the array.