I ran grep -v *[^:] trying to reverse grep a word before a colon, and discovered it runs a command I had run earlier today.
Why?
It will never run a command.
But there are chances that after -v option, the pattern is not quoted. So that is taking all file as input & printing everything ....
Can you please explain the question better if you want us to answer exactly.
The geek is spot on of course. See this example
jonas merzky /tmp : l
-rw------- 1 user group 10 Feb 3 02:10 file_1
-rw------- 1 user group 10 Feb 3 02:10 file_2:
-rw------- 1 user group 10 Feb 3 02:10 file_3:=
with quoting, the grep does what it is expected
jonas merzky /tmp : grep -v '*[^:]'
^C
w/o quoting, your shell will expand the command, and in particular the * will expand to all file names in the directory:
jonas merzky /tmp : echo grep -v *[^:]
grep -v file_1 file_3:=
*[^:] more specifically expands to 'all files which do not end in a colon'. The expanded command is what is being run, with different results than you intented I guess...
I think I know what happened, I copied the output of that command to a file and this grep read the whole file which made it look like it was running the command again.. the command was dtrace, and I had output the stdout to a text file.