CODEWITHSUNDEEP
shellunix
Choi
Choi

Reputation: 523

What is mean that `grep -m 1 ` command in UNIX

I googled this command but there was not.

grep -m 1 "\[{" xxx.txt > xxx.txt

However I typed this command, error didn't occured. Actually, there was not also result of this command.

Please anyone explain me this command's working?

Upvotes: 2

Views: 3112

Answers (1)

l0b0
l0b0

Reputation: 58918

This command reads from and writes to the same file, but not in a left-to-right fashion. In fact > xxx.txt runs first, emptying the file before the grep command starts reading it. Therefore there is no output. You can fix this by storing the result in a temporary file and then renaming that file to the original name.

PS: Some commands, like sed, have an output file option which works around this issue by not relying on shell redirects.

Upvotes: 1

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