< FrankJS />

grep Without cat, and Other Tips

grep is a command commonly used with pipes. This is not the only way it can be used though. One particular practice that appears common, is combining it with cat. This works, but...

If you do this:

$ cat games.txt | grep "chess"

You can probably do this:

$ grep "chess" games.txt

The first way:

1. faster to type

2. uses only one program

3. uses fewer resources / completes faster

Other Tips:

Inverted Matching

The "-v" flag will return everything except lines with the included search string.

-v, --invert-match Invert the sense of matching, to select non-matching lines. (-v is specified by POSIX.)

$ grep -v "something" file.log

Performing multiple rm commands through xargs

$ ls | grep -v ".log" | xargs rm

xargs is a command on Unix and most Unix-like operating systems used to build and execute commands from standard input. It converts input from standard input into arguments to a command.

The above command will remove all files in the current directory except the ones with .log in their filename.

Counting the number of lines with a search term

$ grep -c "something" file.log

Finding only the filenames with the search term

he -l flag will search filenames rather than their contents.

$ grep -l "something" ./*

Finding filenames that don't contain the search term

The -L flag is the inverted matching for filename search.

$ grep -L "something" ./*

Case insensitive search

Use the -i flag to ignore case.

$ grep -i "something" crash.log