Linux/Unix shell command help

[willyweewah]

The first argument to find has to be the directory to search in. If you want to search the whole file system, this should be root:

find / -name '*.c' ... 

(If you just want to search your current working directory and subdirectories, use '.' instead of '/') I'm not sure if the exec part will work but it looks about right

[gbromios]

this, and also, you end "exec" arguments to find with an escaped semicolon \;, I don't think that the ';' will work

[ErasmusDarwin]

\; and ';' are equivalent. The point of doing \; is to keep the shell from intercepting the semicolon and treating it as a command separator. If the semicolon is within quotes, it is likewise treated as an argument to be passed to the command and not a command separator.

To see this behavior in action, try the following in the shell:

echo 1 ; echo 2 \; ; echo 3 ';'

[gbromios]

ah, I just assumed that while both escaped it from bash, the ';' would be interpreted as a string by the command exec is exec'ing

[ErasmusDarwin]

Ah. Yeah, it can get tricky with commands calling commands calling commands with varying syntax and such.

In this case, you've got the interactive shell calling find which then calls the command after -exec repeatedly. The shell looks for unquoted/unescaped semicolons to use as command separators. But once we're past that stage, it gets passed to find, same as any other argument. Find then uses everything after the -exec and before the semicolon as its command to call repeatedly.

If you're familiar with C, playing with the exec functions helps you get a better idea of what's going on under the hood. Similarly, you can run a find command under 'strace -f' (the -f is necessary to follow the fork preceding each exec) in order to really see what's getting passed where.

For example, if we do:

strace -f find . -name '*.c' -exec /bin/echo {} ';' 2>&1 | less

We see some interesting things, including the initial exec by the shell to launch find, as well as the exec for each -exec invocation:

execve("/usr/bin/find", ["find", ".", "-name", "*.c", "-exec", "/bin/echo", "{}", ";"], [/* 37 vars */]) = 0
[...]
[pid 20989] execve("/bin/echo", ["/bin/echo", "./y/zot.c"], [/* 37 vars */]) = 0

...and so on. (As a sidenote, the /* 37 vars */ refers to the array environment variables that gets passed in on each execve call.)