Using grep vs awk

grep will most likely be faster:

# time awk '/USAGE/' imapd.log.1 | wc -l
73832

real    0m2.756s
user    0m2.740s
sys     0m0.020s

# time grep 'USAGE' imapd.log.1 | wc -l
73832

real    0m0.110s
user    0m0.100s
sys     0m0.030s

awk is a interpreted programming language, where as grep is a compiled c-code program (which is additionally optimized towards finding patterns in files).

(Note - I ran both commands twice so that caching would not potentially skew the results)

More details about interpreted languages on wikipedia.

As Stephane has rightly pointed out in comments, your mileage may vary due to the implementation of the grep and awk you use, the operating system it is on and the character set you are processing.

Use the most specific and expressive tool. The tool that best fits your use case is likely to be the fastest.

As a rough guide:

• searching for lines matching a substring or regexp? Use grep.
• selecting certain columns from a simply-delimited file? Use cut.
• performing pattern-based substitutions or ... other stuff sed can reasonably do? Use sed.
• need some combination of the above 3, or printf formatting, or general purpose loops and branches? Use awk.

When only searching for strings, and speed matters, you should almost always use grep. It's orders of magnitude faster than awk when it comes to just gross searching.

source The functional and performance differences of sed, awk and other Unix parsing utilities

UTILITY    OPERATION TYPE      EXECUTION TIME     CHARACTERS PROCESSED PER SECOND
                               (10 ITERATIONS)
-------    --------------      ---------------    -------------------------------
grep       search only         41 sec.            489.3 million
sed        search & replace    4 min. 4 sec.      82.1 million
awk        search & replace    4 min. 46 sec.     69.8 million
Python     search & replace    4 min. 50 sec.     69.0 million
PHP        search & replace    15 min. 44 sec.    21.2 million