Portable way to get file size (in bytes) in shell?

问题

On Linux, I use stat --format="%s" FILE, but Solaris I have access to doesn't have stat command. What should I use then?

I'm writing Bash scripts, and can't really install any new software on the system.

I've considered already using:

perl -e '@x=stat(shift);print $x[7]' FILE

or even:

ls -nl FILE | awk '{print $5}'

But neither of these looks sensible - running Perl just to get file size? Or running 2 commands to do the same?

回答1:

wc -c < filename (short for word count, -c prints the byte count) is a portable, POSIX solution. Only the output format might not be uniform across platforms as some spaces may be prepended (which is the case for Solaris).

Do not omit the input redirection. When the file is passed as an argument, the file name is printed after the byte count.

I was worried it wouldn't work for binary files, but it works OK on both Linux and Solaris. You can try it with wc -c < /usr/bin/wc. Moreover, POSIX utilities are guaranteed to handle binary files, unless specified otherwise explicitly.

回答2:

I ended up writing my own program (really small) to display just the size. More information here: http://fwhacking.blogspot.com/2011/03/bfsize-print-file-size-in-bytes-and.html

The two most clean ways in my opinion with common Linux tools are:

$ stat -c %s /usr/bin/stat
50000

$ wc -c < /usr/bin/wc
36912

But I just don't want to be typing parameters or pipe the output just to get a file size, so I'm using my own bfsize.

回答3:

Even though du usually prints disk usage and not actual data size, GNU coreutils du can print file's "apparent size" in bytes:

du -b FILE

But it won't work under BSD, Solaris, macOS, ...

回答4:

Finally I decided to use ls, and bash array expansion:

TEMP=( $( ls -ln FILE ) )
SIZE=${TEMP[4]}

it's not really nice, but at least it does only 1 fork+execve, and it doesn't rely on secondary programming language (perl/ruby/python/whatever)

回答5:

Cross platform fastest solution (only uses single fork() for ls, doesn't attempt to count actual characters, doesn't spawn unneeded awk, perl, etc).

Tested on MacOS, Linux - may require minor modification for Solaris:

__ln=( $( ls -Lon "$1" ) )
__size=${__ln[3]}
echo "Size is: $__size bytes"

If required, simplify ls arguments, and adjust offset in ${__ln[3]}.

Note: will follow symlinks.

回答6:

BSDs have stat with different options from the GNU coreutils one, but similar capabilities.

stat -f %z <file name>

This works on macOS (tested on 10.12), FreeBSD, NetBSD and OpenBSD.

回答7:

If you use find from GNU fileutils:

size=$( find . -maxdepth 1 -type f -name filename -printf '%s' )

Unfortunately, other implementations of find usually don't support -maxdepth, nor -printf. This is the case for e.g. Solaris and macOS find.

回答8:

When processing ls -n output, as an alternative to ill-portable shell arrays, you can use the positional arguments, which form the only array and are the only local variables in standard shell. Wrap the overwrite of positional arguments in a function to preserve the original arguments to your script or function.

getsize() { set -- $(ls -dn "$1") && echo $5; }
getsize FILE

This splits the output of ln -dn according to current IFS environment variable settings, assigns it to positional arguments and echoes the fifth one. The -d ensures directories are handled properly and the -n assures that user and group names do not need to be resolved, unlike with -l. Also, user and group names containing whitespace could theoretically break the expected line structure; they are usually disallowed, but this possibility still makes the programmer stop and think.

回答9:

You can use find command to get some set of files (here temp files are extracted). Then you can use du command to get the file size of each file in human readable form using -h switch.

find $HOME -type f -name "*~" -exec du -h {} \;

OUTPUT:

4.0K    /home/turing/Desktop/JavaExmp/TwoButtons.java~
4.0K    /home/turing/Desktop/JavaExmp/MyDrawPanel.java~
4.0K    /home/turing/Desktop/JavaExmp/Instream.java~
4.0K    /home/turing/Desktop/JavaExmp/RandomDemo.java~
4.0K    /home/turing/Desktop/JavaExmp/Buff.java~
4.0K    /home/turing/Desktop/JavaExmp/SimpleGui2.java~

回答10:

You first Perl example doesn't look unreasonable to me.

It's for reasons like this that I migrated from writing shell scripts (in bash/sh etc.) to writing all but the most trivial scripts in Perl. I found that I was having to launch Perl for particular requirements, and as I did that more and more, I realised that writing the scripts in Perl was probably a more powerful (in terms of the language and the wide array of libraries available via CPAN) and more efficient way to achieve what I wanted.

Note that other shell-scripting languages (e.g. python/ruby) will no doubt have similar facilities, and you may want to evaluate these for your purposes. I only discuss Perl since that's the language I use and am familiar with.

回答11:

if you have Perl on your Solaris, then use it. Otherwise, ls with awk is your next best bet, since you don't have stat or your find is not GNU find.

回答12:

There is a trick in Solaris I have used, if you ask for the size of more than one file it returns just the total size with no names - so include an empty file like /dev/null as the second file:

eg command fileyouwant /dev/null

I can't rememebr which size command this works for ls/wc/etc - unfortunately I don't have a solaris box to test it.