In efforts to create more manageable scripts that write their own output to only one location themselves (via 'exec > file'), is there a better solution than below for combining stdout redirection + zenity (which in this use relies on piped stdout)?
parent.sh:
#!/bin/bash
exec >> /var/log/parent.out
( true; sh child.sh ) | zenity --progress --pulsate --auto-close --text='Executing child.sh')
[[ "$?" != "0" ]] && exit 1
...
child.sh:
#!/bin/bash
exec >> /var/log/child.out
echo 'Now doing child.sh things..'
...
When doing something like-
sh child.sh | zenity --progress --pulsate --auto-close --text='Executing child.sh'
zenity never receives stdout from child.sh since it is being redirected from within child.sh. Even though it seems to be a bit of a hack, is using a subshell containing a 'true' + execution of child.sh acceptable? Or is there a better way to manage stdout?
I get that 'tee' is acceptable to use in this scenario, though I would rather not have to write out child.sh's logfile location each time I want to execute child.sh.
Your redirection exec > stdout.txt will lead to error.
$ exec > stdout.txt
$ echo hello
$ cat stdout.txt
cat: stdout.txt: input file is output file
You need an intermediary file descriptor.
$ exec 3> stdout.txt
$ echo hello >&3
$ cat stdout.txt
hello
The script should redirect all the output (stdout and stderr) to a log file, and only display stderr to the screen (notifying user if an error happens). The command tee may help but don't know how to write it.
Thanks.
P.S., thanks lihao and konsolebox for the answer, but is there a way to keep the output in order. For example:
$ cat test.sh
echo "to stdout..1"
echo "to stderr..1" >&2
echo "to stdout..2"
echo "to stderr..2" >&2
$ sh test.sh 2>&1 >test.log | tee -a test.log
to stderr..1
to stderr..2
$ cat test.log
to stdout..1
to stdout..2
to stderr..1
to stderr..2
Command: { sh test.sh 2> >(tee /dev/fd/4); } 4>&1 >test.log has the same output.
how about the following:
cmd args 2>&1 >logfile | tee -a logfile
You should map normal stdout to another file descriptor (4), make the file the default output, then use tee to redirect output to the new file descriptor through /dev/fd. Of course you'd need process substitution to pass stderr output to tee:
{ cmd args 2> >(exec tee /dev/fd/4); } 4>&1 >file
If you want to make a general redirection for the script, place this at the beginning of it:
exec 4>&1 >file 2> >(exec tee /dev/fd/4)
You can restore normal output with:
exec >&4 4>&-
Redirecting stdout+stderr such that both get written to a file while still outputting to stdout is simple enough:
cmd 2>&1 | tee output_file
But then now both stdout/stderr from cmd are coming on stdout. I'd like to write stdout+stderr to the same file (so ordering is preserved assuming cmd is single threaded) but then still be able to also separately redirect them, something like this:
some_magic_tee_variant combined_output cmd > >(command-expecting-stdout) 2> >(command-expecting-stderr)
So combined_output contains the both with order preserved, but the command-expecting-stdout only gets stdout and command-expecting-stderr only gets stderr. Basically, I want to log stdout+stderr while still allowing stdout and stderr to be separately redirected and piped. The problem with the tee approach is it globs them together. Is there a way to do this in bash/zsh?
From what I unterstand this is what you are looking for. First I made a litte script to write on stdout and stderr. It looks like this:
$ cat foo.sh
#!/bin/bash
echo foo 1>&2
echo bar
Then I ran it like this:
$ ./foo.sh 2> >(tee stderr | tee -a combined) 1> >(tee stdout | tee -a combined)
foo
bar
The results in my bash look like this:
$ cat stderr
foo
$ cat stdout
bar
$ cat combined
foo
bar
Note that the -a flag is required so the tees don't overwrite the other tee's content.
{ { cmd | tee out >&3; } 2>&1 | tee err >&2; } 3>&1
Or, to be pedantic:
{ { cmd 3>&- | tee out >&3 2> /dev/null; } 2>&1 | tee err >&2 3>&- 2> /dev/null; } 3>&1
Note that it's futile to try and preserve order. It is basically impossible. The only solution would be to modify "cmd" or use some LD_PRELOAD or gdb hack,
Order can indeed be preserved. Here's an example which captures the standard output and error, in the order in which they are generated, to a logfile, while displaying only the standard error on any terminal screen you like. Tweak to suit your needs.
1.Open two windows (shells)
2.Create some test files
touch /tmp/foo /tmp/foo1 /tmp/foo2
3.In window1:
mkfifo /tmp/fifo
</tmp/fifo cat - >/tmp/logfile
4.Then, in window2:
(ls -l /tmp/foo /tmp/nofile /tmp/foo1 /tmp/nofile /tmp/nofile; echo successful test; ls /tmp/nofile1111) 2>&1 1>/tmp/fifo | tee /tmp/fifo 1>/dev/pts/1
Where /dev/pts/1 can be whatever terminal display you want. The subshell runs some "ls" and "echo" commands in sequence, some succeed (providing stdout) and some fail (providing stderr) in order to generate a mingled stream of output and error messages, so that you can verify the correct ordering in the log file.
Here's how I do it:
exec 3>log ; example_command 2>&1 1>&3 | tee -a log ; exec 3>&-
Worked Example
bash$ exec 3>log ; { echo stdout ; echo stderr >&2 ; } 2>&1 1>&3 | \
tee -a log ; exec 3>&-
stderr
bash$ cat log
stdout
stderr
Here's how that works:
exec 3>log sets up file descriptor 3 to redirect into the file called log, until further notice.
example_command to make this a working example, I used { echo stdout ; echo stderr >&2 ; }. Or you could use ls /tmp doesnotexist to provide output instead.
Need to jump ahead to the pipe | at this point because bash does it first. The pipe sets up a pipe and redirects the file descriptor 1 into this pipe. So now, STDOUT is going into the pipe.
Now we can go back to where we were next in our left-to-right interpretation: 2>&1 this says errors from the program are to go to where STDOUT currently points, i.e. into the pipe we just set up.
1>&3 means STDOUT is redirected into file descriptor 3, which we earlier set up to output to the log file. So STDOUT from the command just goes into the log file, not to the terminal's STDOUT.
tee -a log takes it's input from the pipe (which you'll remember is now the errors from the command), and outputs it to STDOUT and also appends it to the log file.
exec 3>&- closes the file descriptor 3.
Victor Sergienko's comment is what worked for me, adding exec to the front of it makes this work for the entire script (instead of having to put it after individual commands)
exec 2> >(tee -a output_file >&2) 1> >(tee -a output_file)
I have two shell scripts, one that serves as the main "program" and another that serves as a "library."
In several places in the "program," I'll do something like: log "$thing" >> "$logfile", where log is a function defined in the "library."
# program.sh
logfile="log.txt"
stuff="hahah heheh hoho"
. library.sh
for thing in $stuff; do
log "$thing" >> "$logfile"
done
My question: Is there a way to redirect some of the output from the function back to the terminal without using stderr?
# library.sh
log () {
# This gets written to the log
echo "`date --rfc-3339=seconds`: $1"
# How to write this to the terminal *without* using stderr?
echo "Info: Message written to log." >&2
}
I want to avoid the use of stderr because in my actual program, there's an option to redirect errors to a file, but the messages I want to send to the terminal are informational, not errors, and should always show up on the terminal.
Open /dev/tty on another FD.
exec 0< /dev/null
exec 1> /dev/null
exec 2> /dev/null
exec 3> /dev/tty
echo 'Hello, World!' >&3
You can write directly to /dev/tty each time you want to write to the terminal:
echo "hello world" > /dev/tty
For a small example:
$ cat writer.sh
#!/bin/sh
echo "standard output"
echo "standard error" >&2
echo "direct to terminal" > /dev/tty
$ ./writer.sh > /tmp/out 2> /tmp/err
direct to terminal
$ cat /tmp/out
standard output
$ cat /tmp/err
standard error
$
I have a script which will be run interactively by non-technical users. The script writes status updates to STDOUT so that the user can be sure that the script is running OK.
I want both STDOUT and STDERR redirected to the terminal (so that the user can see that the script is working as well as see if there was a problem). I also want both streams redirected to a log file.
I've seen a bunch of solutions on the net. Some don't work and others are horribly complicated. I've developed a workable solution (which I'll enter as an answer), but it's kludgy.
The perfect solution would be a single line of code that could be incorporated into the beginning of any script that sends both streams to both the terminal and a log file.
EDIT: Redirecting STDERR to STDOUT and piping the result to tee works, but it depends on the users remembering to redirect and pipe the output. I want the logging to be fool-proof and automatic (which is why I'd like to be able to embed the solution into the script itself.)
Use "tee" to redirect to a file and the screen. Depending on the shell you use, you first have to redirect stderr to stdout using
./a.out 2>&1 | tee output
or
./a.out |& tee output
In csh, there is a built-in command called "script" that will capture everything that goes to the screen to a file. You start it by typing "script", then doing whatever it is you want to capture, then hit control-D to close the script file. I don't know of an equivalent for sh/bash/ksh.
Also, since you have indicated that these are your own sh scripts that you can modify, you can do the redirection internally by surrounding the whole script with braces or brackets, like
#!/bin/sh
{
... whatever you had in your script before
} 2>&1 | tee output.file
Approaching half a decade later...
I believe this is the "perfect solution" sought by the OP.
Here's a one liner you can add to the top of your Bash script:
exec > >(tee -a $HOME/logfile) 2>&1
Here's a small script demonstrating its use:
#!/usr/bin/env bash
exec > >(tee -a $HOME/logfile) 2>&1
# Test redirection of STDOUT
echo test_stdout
# Test redirection of STDERR
ls test_stderr___this_file_does_not_exist
(Note: This only works with Bash. It will not work with /bin/sh.)
Adapted from here; the original did not, from what I can tell, catch STDERR in the logfile. Fixed with a note from here.
The Pattern
the_cmd 1> >(tee stdout.txt ) 2> >(tee stderr.txt >&2 )
This redirects both stdout and stderr separately, and it sends separate copies of stdout and stderr to the caller (which might be your terminal).
In zsh, it will not proceed to the next statement until the tees have finished.
In bash, you may find that the final few lines of output appear after whatever statement comes next.
In either case, the right bits go to the right places.
Explanation
Here's a script (stored in ./example):
#! /usr/bin/env bash
the_cmd()
{
echo out;
1>&2 echo err;
}
the_cmd 1> >(tee stdout.txt ) 2> >(tee stderr.txt >&2 )
Here's a session:
$ foo=$(./example)
err
$ echo $foo
out
$ cat stdout.txt
out
$ cat stderr.txt
err
Here's how it works:
Both tee processes are started, their stdins are assigned to file descriptors. Because they're enclosed in process substitutions, the paths to those file descriptors are substituted in the calling command, so now it looks something like this:
the_cmd 1> /proc/self/fd/13 2> /proc/self/fd/14
the_cmd runs, writing stdout to the first file descriptor, and stderr to the second one.
In the bash case, once the_cmd finishes, the following statement happens immediately (if your terminal is the caller, then you will see your prompt appear).
In the zsh case, once the_cmd finishes, the shell waits for both of the tee processes to finish before moving on. More on this here.
The first tee process, which is reading from the_cmd's stdout, writes a copy of that stdout back to the caller because that's what tee does. Its outputs are not redirected, so they make it back to the caller unchanged
The second tee process has it's stdout redirected to the caller's stderr (which is good, because it's stdin is reading from the_cmd's stderr). So when it writes to its stdout, those bits go to the caller's stderr.
This keeps stderr separate from stdout both in the files and in the command's output.
If the first tee writes any errors, they'll show up in both the stderr file and in the command's stderr, if the second tee writes any errors, they'll only show up only in the terminal's stderr.
the to redirect stderr to stdout append this at your command: 2>&1
For outputting to terminal and logging into file you should use tee
Both together would look like this:
mycommand 2>&1 | tee mylogfile.log
EDIT: For embedding into your script you would do the same. So your script
#!/bin/sh
whatever1
whatever2
...
whatever3
would end up as
#!/bin/sh
( whatever1
whatever2
...
whatever3 ) 2>&1 | tee mylogfile.log
EDIT:
I see I got derailed and ended up answering a different question from the one asked. The answer to the real question is at the bottom of Paul Tomblin's answer. (If you want to enhance that solution to redirect stdout and stderr separately for some reason, you could use the technique I describe here.)
I've been wanting an answer that preserves the distinction between stdout and stderr.
Unfortunately all of the answers given so far that preserve that distinction
are race-prone: they risk programs seeing incomplete input, as I pointed out in comments.
I think I finally found an answer that preserves the distinction,
is not race prone, and isn't terribly fiddly either.
First building block: to swap stdout and stderr:
my_command 3>&1 1>&2 2>&3-
Second building block: if we wanted to filter (e.g. tee) only stderr,
we could accomplish that by swapping stdout&stderr, filtering, and then swapping back:
{ my_command 3>&1 1>&2 2>&3- | stderr_filter;} 3>&1 1>&2 2>&3-
Now the rest is easy: we can add a stdout filter, either at the beginning:
{ { my_command | stdout_filter;} 3>&1 1>&2 2>&3- | stderr_filter;} 3>&1 1>&2 2>&3-
or at the end:
{ my_command 3>&1 1>&2 2>&3- | stderr_filter;} 3>&1 1>&2 2>&3- | stdout_filter
To convince myself that both of the above commands work, I used the following:
alias my_command='{ echo "to stdout"; echo "to stderr" >&2;}'
alias stdout_filter='{ sleep 1; sed -u "s/^/teed stdout: /" | tee stdout.txt;}'
alias stderr_filter='{ sleep 2; sed -u "s/^/teed stderr: /" | tee stderr.txt;}'
Output is:
...(1 second pause)...
teed stdout: to stdout
...(another 1 second pause)...
teed stderr: to stderr
and my prompt comes back immediately after the "teed stderr: to stderr", as expected.
Footnote about zsh:
The above solution works in bash (and maybe some other shells, I'm not sure), but it doesn't work in zsh. There are two reasons it fails in zsh:
the syntax 2>&3- isn't understood by zsh; that has to be rewritten
as 2>&3 3>&-
in zsh (unlike other shells), if you redirect a file descriptor
that's already open, in some cases (I don't completely understand how it decides) it does a built-in tee-like behavior instead. To avoid this, you have to close each fd prior to
redirecting it.
So, for example, my second solution has to be rewritten for zsh as {my_command 3>&1 1>&- 1>&2 2>&- 2>&3 3>&- | stderr_filter;} 3>&1 1>&- 1>&2 2>&- 2>&3 3>&- | stdout_filter (which works in bash too, but is awfully verbose).
On the other hand, you can take advantage of zsh's mysterious built-in implicit teeing to get a much shorter solution for zsh, which doesn't run tee at all:
my_command >&1 >stdout.txt 2>&2 2>stderr.txt
(I wouldn't have guessed from the docs I found that the >&1 and 2>&2 are the thing that trigger zsh's implicit teeing; I found that out by trial-and-error.)
Use the tee program and dup stderr to stdout.
program 2>&1 | tee > logfile
Use the script command in your script (man 1 script)
Create a wrapper shellscript (2 lines) that sets up script() and then calls exit.
Part 1: wrap.sh
#!/bin/sh
script -c './realscript.sh'
exit
Part 2: realscript.sh
#!/bin/sh
echo 'Output'
Result:
~: sh wrap.sh
Script started, file is typescript
Output
Script done, file is typescript
~: cat typescript
Script started on fr. 12. des. 2008 kl. 18.07 +0100
Output
Script done on fr. 12. des. 2008 kl. 18.07 +0100
~:
I created a script called "RunScript.sh". The contents of this script is:
${APP_HOME}/${1}.sh ${2} ${3} ${4} ${5} ${6} 2>&1 | tee -a ${APP_HOME}/${1}.log
I call it like this:
./RunScript.sh ScriptToRun Param1 Param2 Param3 ...
This works, but it requires the application's scripts to be run via an external script. It's a bit kludgy.
A year later, here's an old bash script for logging anything. For example,
teelog make ... logs to a generated log name (and see the trick for logging nested makes too.)
#!/bin/bash
me=teelog
Version="2008-10-9 oct denis-bz"
Help() {
cat <<!
$me anycommand args ...
logs the output of "anycommand ..." as well as displaying it on the screen,
by running
anycommand args ... 2>&1 | tee `day`-command-args.log
That is, stdout and stderr go to both the screen, and to a log file.
(The Unix "tee" command is named after "T" pipe fittings, 1 in -> 2 out;
see http://en.wikipedia.org/wiki/Tee_(command) ).
The default log file name is made up from "command" and all the "args":
$me cmd -opt dir/file logs to `day`-cmd--opt-file.log .
To log to xx.log instead, either export log=xx.log or
$me log=xx.log cmd ...
If "logdir" is set, logs are put in that directory, which must exist.
An old xx.log is moved to /tmp/\$USER-xx.log .
The log file has a header like
# from: command args ...
# run: date pwd etc.
to show what was run; see "From" in this file.
Called as "Log" (ln -s $me Log), Log anycommand ... logs to a file:
command args ... > `day`-command-args.log
and tees stderr to both the log file and the terminal -- bash only.
Some commands that prompt for input from the console, such as a password,
don't prompt if they "| tee"; you can only type ahead, carefully.
To log all "make" s, including nested ones like
cd dir1; \$(MAKE)
cd dir2; \$(MAKE)
...
export MAKE="$me make"
!
# See also: output logging in screen(1).
exit 1
}
#-------------------------------------------------------------------------------
# bzutil.sh denisbz may2008 --
day() { # 30mar, 3mar
/bin/date +%e%h | tr '[A-Z]' '[a-z]' | tr -d ' '
}
edate() { # 19 May 2008 15:56
echo `/bin/date "+%e %h %Y %H:%M"`
}
From() { # header # from: $* # run: date pwd ...
case `uname` in Darwin )
mac=" mac `sw_vers -productVersion`"
esac
cut -c -200 <<!
${comment-#} from: $#
${comment-#} run: `edate` in $PWD `uname -n` $mac `arch`
!
# mac $PWD is pwd -L not -P real
}
# log name: day-args*.log, change this if you like --
logfilename() {
log=`day`
[[ $1 == "sudo" ]] && shift
for arg
do
log="$log-${arg##*/}" # basename
(( ${#log} >= 100 )) && break # max len 100
done
# no blanks etc in logfilename please, tr them to "-"
echo $logdir/` echo "$log".log | tr -C '.:+=[:alnum:]_\n' - `
}
#-------------------------------------------------------------------------------
case "$1" in
-v* | --v* )
echo "$0 version: $Version"
exit 1 ;;
"" | -* )
Help
esac
# scan log= etc --
while [[ $1 == [a-zA-Z_]*=* ]]; do
export "$1"
shift
done
: ${logdir=.}
[[ -w $logdir ]] || {
echo >&2 "error: $me: can't write in logdir $logdir"
exit 1
}
: ${log=` logfilename "$#" `}
[[ -f $log ]] &&
/bin/mv "$log" "/tmp/$USER-${log##*/}"
case ${0##*/} in # basename
log | Log ) # both to log, stderr to caller's stderr too --
{
From "$#"
"$#"
} > $log 2> >(tee /dev/stderr) # bash only
# see http://wooledge.org:8000/BashFAQ 47, stderr to a pipe
;;
* )
#-------------------------------------------------------------------------------
{
From "$#" # header: from ... date pwd etc.
"$#" 2>&1 # run the cmd with stderr and stdout both to the log
} | tee $log
# mac tee buffers stdout ?
esac
This question seems has not been gracefully solved yet.
Everytime I search "how to output to stdout and stderr at same time", google directs me to this post.
Today, I finally found a simple & effective way to solve almost all these kind of needs.
The essential idea is the tee command which can print to multiple output at same time, and linux-specific /proc/self/fd/{1,2,...} to represent stdout, stderr...
print stdin to both stdout and stderr
tee /proc/self/fd/2
print stdin to both stdout and stderr, and file
tee /proc/self/fd/2 file
Hope this be helpful.
Here is a solution working for bash by redirection, by combining the solution of "kvantour, MatrixManAtYrService" and "Jason Sydes":
#!/bin/bash
exec 1> >(tee x.log) 2> >(tee x.err >&2)
echo "test for log"
echo "test for err" 1>&2
Save the script above as x.sh. After running ./x.sh, the x.log only include the stdout, while the x.err only include the stderr.