为什么运行带有双引号的awk会中断，但可以使用单引号？

Question

I noticed when running a command that this statement doesn't recognize the delimiter

awk -F',' "{print $4}" wtd.csv

However, this one does.

awk -F',' '{print $4}' wtd.csv

Any reason why? I'm sure this is part of some general bash rule I'm forgetting.

Answer 1

If you're using double quotes, $4 will get replaced by Bash (probably with the empty string). You'd need to escape the $ to use it in double quotes.

Example where this also is happening:

[thom@lethe ~]$ echo '$4'
$4
[thom@lethe ~]$ echo "$4"

[thom@lethe ~]$ echo "\$4"
$4

Answer 2

You are forgetting that double-quotes allow bash variable interpolation. In this case it tries to replace $4 with the fourth argument to the shell which is usually empty.

The single-quotes prevent bash interpolation and passes the literal $4 to awk.

Answer 3

You'll have identical results with:

awk -F',' '{print $4}' wtd.csv
awk -F',' "{print \$4}" wtd.csv