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I'm not sure I understand your question, but your code can be optimised to:

awk 'NR==FNR{a[$0]="";next}; !($0 in a)' foo/file bar/file > tmp 

(yours had issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh93. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ... 

I'm not sure I understand your question, but your code can be optimised to:

awk '!x{a[$0];next}; !($0 in a)' foo/file x=1 bar/file > tmp 

(yours had issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh93. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ... 

I'm not sure I understand your question, but your code can be optimised to:

awk 'NR==FNR{a[$0]="";next}!($0 in a)' foo/file bar/file > tmp 

(yours had issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ... 

I'm not sure I understand your question, but your code can be optimised to:

awk 'NR==FNR{a[$0]="";next}; !($0 in a)' foo/file bar/file > tmp 

(yours had issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh93. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ... 

I'm not sure I understand your question, but your code can be optimised to:

awk 'NR==FNR{a[$0]="";next}!($0 in a)' foo/file bar/file > tmp 

(yours add issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ... 

I'm not sure I understand your question, but your code can be optimised to:

awk 'NR==FNR{a[$0]="";next}!($0 in a)' foo/file bar/file > tmp 

(yours had issues for empty lines or lines resolving to "0" in them I think)

If the files are sorted, you could do:

comm -13 foo/file bar/file > tmp 

If they're not (ksh. zsh or bash syntax):

comm -13 <(sort foo/file) <(sort bar/file) > tmp 

(not necessarily faster than the awk solution)

Also, especially with GNU awk, you may get better performance by setting the locale to C/POSIX:

LC_ALL=C awk ...