Escaping backslashes in NSTask arguments?

Question

I am trying to get the latest modification date in a directory tree. This works fine in terminal:

find . ! -path "*.git*" -exec stat -f "%m" \{} \; | sort -n -r | head -1

But when I try this with NSTask I get

find: -exec: no terminating ";" or "+"

In the args array for NSTask which I am using, I escaped the backslashes:

NSArray *args = @[@".", 
                  @"!", 
                  @"-path", 
                  @"*.git*", 
                  @"-exec", 
                  @"stat", 
                  @"-f", 
                  @"%m", 
                  @"\\{}", 
                  @"\\;", 
                  @"|", 
                  @"sort", 
                  @"-n", 
                  @"-r", 
                  @"|", 
                  @"head", 
                  @"-1"];

So, what am I missing here? I also tried to remove the backslahes all together, but that gave me a "find: |: unknown primary or operator" error.

I think you should make one nstask for each of the command you are using, then pipe their standard out to the next command standard in. — JoshRagem, Dec 20 '12 at 16:37

score 1 · Accepted Answer · answered Dec 20 '12 at 16:47

Thanks for the hints guys. I've split it up and get more response now. When running the command without backslashes & without the sort & head I do get results.

NSArray *args = @[@".", 
              @"!", 
              @"-path", 
              @"*.git*", 
              @"-exec", 
              @"stat", 
              @"-f", 
              @"%m", 
              @"{}", 
              @";"];

So it looks like NSTask should not be fed '|' characters. I'll just so the sorting etc. in objc.

JoshRagem · Answer 2 · 2012-12-20T16:49:22.370

You actually have three command line programs that you call with

find . ! -path "*.git*" -exec stat -f "%m" \{} \; | sort -n -r | head -1

find, sort, and head.

You should make an nstask for each of theses commands--link the stdout of find to the stdin of sort and then do the same with sort and head.

According to the docs, you should be able the set an NSPipe as the out of one and the in of another, if this doesn't work you could just pull the results back and pass them to next one manually.

Though I have not verified it, I don't think you need the backslash escapes because this does not go through your terminal to launch these programs.

score 0 · Answer 3 · answered Dec 20 '12 at 17:42

Figured out another way of doing this.

I now run an NSTask command /bin/sh with the arguments:

NSArray *args = @[@"-c", 
                  @"/usr/bin/find . ! -path \"*.git*\" -exec stat -f %%m \\{} \\; | sort -n -r | head -1"];

Credits to http://borkware.com/quickies/single?id=130

Escaping backslashes in NSTask arguments?

3 Answers3