On Wed, May 29, 2002 at 11:29:29AM -0700, Peter Jay Salzman wrote:
> begin nbs <[EMAIL PROTECTED]>
> > strace lsof 2>&1 1> /dev/null | grep
>
> ok, haven't tried this, but this looks to me like:
>
> put stderr into stdout
> redirect stdout (and therefore stderr) into /dev/null
> pipe stdout (which should be null) to grep.
The order of operation of file operators is right to left.
So the first operation "| grep" spawns a copy of grep on the
stdout of a future output of a new pipe. The second "1> /dev/null"
takes stdout and throws it away. The third "2>&1" takes stderr and
redirects it to stdout.
The command line you are looking for if you want stderr grepped
and stdout to still be displayed is some variant of this:
( strace ls -R / 2>&1 1>&3 | grep open; ) 3>&1
(which will show you each open call and the output that ls prints
after each, alternating... sample output below, kinda cool).
here is a breakdown of the command-line above in order of operation...
=========
"( ... ) 3>&1"
open a file descriptor 3 and attach it to my current stdout.
"( ... )"
run the following in a subshell
"... | ..."
run the thing on the left and direct it's stdout into the thing on the
right.
"grep open"
look for the word "open" in my stdin.
"1>&3"
redirect stdout to file descriptor 3.
"2>&1"
redirect stderr to stdout.
"strace ls -R /"
strace the output of "ls -R /"
=========
Note that the sample command above is just a sample, if you really
wanted all the times strace detected an open call then give strace the
option "-e open" ... which is much better.
sample output from the new command:
=========
msimons@star:~/debian$ ( strace ls -R / 2>&1 1>&3 | grep open; ) 3>&1
open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 4
open("/lib/librt.so.1", O_RDONLY) = 4
open("/lib/libc.so.6", O_RDONLY) = 4
open("/lib/libpthread.so.0", O_RDONLY) = 4
open("/dev/null", O_RDONLY|O_NONBLOCK|O_DIRECTORY) = -1 ENOTDIR (Not a directory)
open("/", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 4
open("/etc/mtab", O_RDONLY) = 4
open("/proc/meminfo", O_RDONLY) = 4
/:
bin cdrom etc ibm2 lost+found proc share tmp vmlinuz
boot cdrom0 floppy initrd mnt root test usr vmlinuz.old
brick dev home lib opt sbin thor var
open("/bin", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 4
/bin:
arch dd fuser ls netstat sed true zforce
ash df grep lspci pidof setserial umount zgrep
bash dir gunzip mkdir ping sh uname zless
cat dmesg gzexe mknod ps sleep uncompress zmore
chgrp dnsdomainname gzip mktemp pwd stty vdir znew
chmod echo hostname more rbash su zcat
chown ed kill mount readlink sync zcmp
cp egrep ln mt rm tar zdiff
cpio false loadkeys mt-gnu rmdir tempfile zegrep
date fgrep login mv run-parts touch zfgrep
open("/boot", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 4
/boot:
System.map-2.4.18 boot-menu.b boot.b map
System.map-2.4.18-bf2.4 boot-text.b chain.b os2_d.b
boot-bmp.b boot.0200 config-2.4.18 vmlinuz-2.4.18
boot-compat.b boot.0801 config-2.4.18-bf2.4 vmlinuz-2.4.18-bf2.4
=========
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