5 SC2146

Tom Grace edited this page 2024-09-19 09:48:04 +01:00

Table of Contents

• This action ignores everything before the -o. Use ( ) to group.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions

This action ignores everything before the -o. Use \( \) to group.

Problematic code:

find . -name '*.avi' -o -name '*.mkv' -exec cp {} /media \;

Correct code:

find . \( -name '*.avi' -o -name '*.mkv' \) -exec cp {} /media \;

Note that the space between \( and -name in this command is significant.

Rationale:

In find, two predicates with no operator between them is considered a logical, short-circuiting AND (as if using -a). E.g., -name '*.mkv' -exec .. is the same as -name '*.mkv' -a -exec ...

-a has higher precedence than -o, so -name '*.avi' -o -name '*.mkv' -a -exec .. is equivalent to -name '*.avi' -o \( -name '*.mkv' -a -exec .. \).

In other words, the problematic code means "if name matches *.avi, do nothing. Otherwise, if it matches *.mkv, execute a command.".

In the correct code, we use \( \) to group to get the evaluation order we want. The correct code means "if name matches *.avi or *.mkv, then execute a command", which was what was intended.

Exceptions

If you're aware of this, you can either ignore this error or group to make it explicit. For example, to decompress all gz files except tar.gz, you can use:

find . -name '*.tar.gz' -o \( -name '*.gz' -exec gzip -d {} + \)

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