Find Command – When Will `find . -exec COMMAND {} +` Execute COMMAND Multiple Times?

find

If I do 

find . -exec echo {} +

it prints all paths in one line, i.e. command echo is only executed once.

But according to man find, 

-exec command {} +
    ... the number of invocations of the command will 
be much  less  than  the  number  of matched files. ...

It seems that in some circumstances the command will be executed multiple times. Am I right? Please exemplify.

Best Answer

POSIX defined find -exec utility_name [argument ...] {} + as:

The end of the primary expression shall be punctuated by a <semicolon> or by a <plus-sign>. Only a <plus-sign> that immediately follows an argument containing only the two characters "{}" shall punctuate the end of the primary expression. Other uses of the <plus-sign> shall not be treated as special. If the primary expression is punctuated by a <semicolon>, the utility utility_name shall be invoked once for each pathname and the primary shall evaluate as true if the utility returns a zero value as exit status. A utility_name or argument containing only the two characters "{}" shall be replaced by the current pathname. If a utility_name or argument string contains the two characters "{}", but not just the two characters "{}", it is implementation-defined whether find replaces those two characters or uses the string without change.

If the primary expression is punctuated by a <plus-sign>, the primary shall always evaluate as true, and the pathnames for which the primary is evaluated shall be aggregated into sets. The utility utility_name shall be invoked once for each set of aggregated pathnames. Each invocation shall begin after the last pathname in the set is aggregated, and shall be completed before the find utility exits and before the first pathname in the next set (if any) is aggregated for this primary, but it is otherwise unspecified whether the invocation occurs before, during, or after the evaluations of other primaries. If any invocation returns a non-zero value as exit status, the find utility shall return a non-zero exit status. An argument containing only the two characters "{}" shall be replaced by the set of aggregated pathnames, with each pathname passed as a separate argument to the invoked utility in the same order that it was aggregated. The size of any set of two or more pathnames shall be limited such that execution of the utility does not cause the system's {ARG_MAX} limit to be exceeded. If more than one argument containing the two characters "{}" is present, the behavior is unspecified.

When length set of file name you found exceed system ARG_MAX, the command is executed.

You can get ARG_MAX using getconf:

$ getconf ARG_MAX
2097152

On some system, actual value of ARG_MAX can be different, you can refer here for more details.

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