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Re: Problem with cp (copy)

From: Alfred M. Szmidt
Subject: Re: Problem with cp (copy)
Date: Wed, 22 Jan 2003 15:38:25 +0100

Please read the Coreutils FAQ, it describes your problem in detail [1].

Argument list too long

I tried to move about 5000 files with mv, but it said:

  bash: /bin/mv: Argument list too long

The UNIX operating system traditionally has a fixed limit for the amount of 
memory that can be used for a program environment and argument list combined. 
You can use getconf to return that limit. On my Linux system (2.2.12) that 
amount is 128k. On my HP-UX system (11.0) that amount is 2M. It can vary per 
operating system. POSIX only requires 20k which was the traditional value used 
for probably 20 years. Newer operating systems releases usually increase that 

  getconf ARG_MAX

Note that your message came from "bash" your shell command line interpreter. 
Its job is to expand command line wildcard characters that match filenames. It 
expands them before any program can see them. This is therefore common to all 
programs on most UNIX-like operating systems. It cannot exceed the OS limit of 
ARG_MAX and if it tries to do so the error "Argument list too long" is returned 
to the shell and the shell returns it to you.

This is not a bug in 'mv' or other utilities nor is it a bug in 'bash' or any 
other shell. It is an architecture limitation of UNIX-like operating systems. 
The 'mv' program was prevented by the OS from running and the shell is just the 
one in the middle reporting the problem. The shell tried to load the program 
but the OS ran out of space. However, this problem is one that is easily worked 
around using the supplied utilities. Please review the documentation on 'find' 
and 'xargs' for one possible combination of programs that work well.

You might think about increasing the value of ARG_MAX but I advise against it. 
Any limit, even if large, is still a limit. As long as it exists then it should 
be worked around for robust script operation. On the command line most of us 
ignore it unless we exceed it at which time we fall back to more robust methods.

Here is an example using chmod where exceeding ARG_MAX argument length is 

  find htdocs -name '*.html' -print0 | xargs -0 chmod a+r

Read the previous question for another facet of this problem. 

[1]: http://www.gnu.org/software/fileutils/doc/faq/#Argument%20list%20too%20long

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