I know this much:
$ command 2>> error
$ command 1>> output
Is there any way I can output the stderr to the error file and output stdout to the output file in the same line of bash?
Just add them in one line command 2>> error 1>> output
However, note that >> is for appending if the file already has data. Whereas, > will overwrite any existing data in the file.
So, command 2> error 1> output if you do not want to append.
Just for completion's sake, you can write 1> as just > since the default file descriptor is the output. so 1> and > is the same thing.
So, command 2> error 1> output becomes, command 2> error > output
Try this:
your_command 2>stderr.log 1>stdout.log
More information
The numerals 0 through 9 are file descriptors in bash.
0 stands for standard input, 1 stands for standard output, 2 stands for standard error. 3 through 9 are spare for any other temporary usage.
Any file descriptor can be redirected to a file or to another file descriptor using the operator >. You can instead use the operator >> to appends to a file instead of creating an empty one.
Usage:
file_descriptor > filename
file_descriptor > &file_descriptor
Please refer to Advanced Bash-Scripting Guide: Chapter 20. I/O Redirection.
Like that:
$ command >>output 2>>error
Or if you like to mix outputs (stdout & stderr) in one single file you may want to use:
command > merged-output.txt 2>&1
Multiple commands' output can be redirected. This works for either the command line or most usefully in a bash script. The -s directs the password prompt to the screen.
Hereblock cmds stdout/stderr are sent to seperate files and nothing to display.
sudo -s -u username <<'EOF' 2>err 1>out
ls; pwd;
EOF
Hereblock cmds stdout/stderr are sent to a single file and display.
sudo -s -u username <<'EOF' 2>&1 | tee out
ls; pwd;
EOF
Hereblock cmds stdout/stderr are sent to separate files and stdout to display.
sudo -s -u username <<'EOF' 2>err | tee out
ls; pwd;
EOF
Depending on who you are(whoami) and username a password may or may not be required.
When I use
$ ls | tee log.txt
I get correct, expected result: log.txt keeps 'ls' output.
I need to save output of the command:
$ svnadmin dump MyRepo -r1:r2 > dumpfile
* Dumped revision 1.
* Dumped revision 2.
Where "$ svnadmin .." is command and
"* Dumped .." are outputs
So, the question itself. When I run the command:
$ svnadmin dump MyRepo -r1:r2 > dumpfile | tee log.txt
* Dumped revision 1.
* Dumped revision 2.
log.txt has 0 size
TL;DR -- Try this one:
svnadmin dump MyRepo -r1:r2 2>&1 > dumpfile | tee log.txt
Explanation: Each command has three connected "standard streams": Standard Input (STDIN, filehandle 0), Standard Output (STDOUT, 1) and Standard Error (STDERR, 2). Usually commands ouput their "data" on STDOUT and errors on STDERR.
A simple command like ls has all three of them connected to the console. Because both STDOUT and STDERR are connected to the console the output of the command is interleaved.
A "pipe" like ls | tee log.txt redirects STDOUT of the first command to STDIN of the second command. No more - no less. Therefore all other streams are still connected to the console. Should the ls part produce error messages they will be written to the console, not to the file! But your ls example did not output any errors so you didn't notice.
After the pipe is setup the shell evaluates the other redirection operator of the first command -- from left to right.
Therefore svnadmin dump > dumpfile | tee log.txt will redirect STDOUT of svnadmin to dumpfile leaving effectively no data for the tee command because that's a redirection, not a copy.
svnadmin dump MyRepo 2>&1 > dumpfile | tee log.txt adds another redirection step. It reads "make filehandle 2 (STDERR) a copy of the filehandle 1 (STDOUT)" which is the pipe at this point. Writing to either STDOUT or STDERR will write to the pipe. But after that the > dumpfile redirection is applied and STDOUT is redirected to the file.
You can read all this (and much more) in the shell's manual. For bash it is in the section REDIRECTION.
If I use this
cmd 2>/var/error.log
Then my error goes to that file but then I can't see on screen.
Is there any way I can simultaneously show it on screen as well as send to file?
This will display both stdout and stderr on the terminal while only sending stderr to err.log:
cmd 2> >(tee err.log >&2)
>(...) is process substitution. (The space between the two consecutive > is essential.) This sends stderr and only stderr to the tee command.
The >&2 causes the error messages remain in stderr. This would be important, for example, if this line occurs inside some script whose stdin or stderr is being redirected. (Hat tip: Chepner.)
cmd 2>&1 | tee /tmp/error.log
Nohup redirects stderr to stdout if it points to a terminal. But I want to retain stderr output to the terminal
Is there a way to accomplish that? Is there an alternative?
I don't know if I understood correctly or not.
you mean that you don't want to see the error in terminal?
if yes:
if you want to save the error in file:
nohup command 2> file.txt
if you don't need the errors:
nohup command 2> /dev/null
2 means the error output of command
2> file.txt means write the error output to the file.txt
Just redirect it somewhere else, so it's not the terminal:
nohup bash -c 'echo OUT ; echo ERR >& 2' 2> err
You can redirect the stderr back to stdout instead of to a file to keep the output in the terminal, but it doesn't make much sense: nohup is for situations where the terminal might get lost, in which case you'll lose the stderr.
nohup bash -c 'echo OUT ; echo ERR >& 2' 2> >(cat)
I know how to use tee to write the output (standard output) of aaa.sh to bbb.out, while still displaying it in the terminal:
./aaa.sh | tee bbb.out
How would I now also write standard error to a file named ccc.out, while still having it displayed?
I'm assuming you want to still see standard error and standard output on the terminal. You could go for Josh Kelley's answer, but I find keeping a tail around in the background which outputs your log file very hackish and cludgy. Notice how you need to keep an extra file descriptor and do cleanup afterward by killing it and technically should be doing that in a trap '...' EXIT.
There is a better way to do this, and you've already discovered it: tee.
Only, instead of just using it for your standard output, have a tee for standard output and one for standard error. How will you accomplish this? Process substitution and file redirection:
command > >(tee -a stdout.log) 2> >(tee -a stderr.log >&2)
Let's split it up and explain:
> >(..)
>(...) (process substitution) creates a FIFO and lets tee listen on it. Then, it uses > (file redirection) to redirect the standard output of command to the FIFO that your first tee is listening on.
The same thing for the second:
2> >(tee -a stderr.log >&2)
We use process substitution again to make a tee process that reads from standard input and dumps it into stderr.log. tee outputs its input back on standard output, but since its input is our standard error, we want to redirect tee's standard output to our standard error again. Then we use file redirection to redirect command's standard error to the FIFO's input (tee's standard input).
See Input And Output
Process substitution is one of those really lovely things you get as a bonus of choosing Bash as your shell as opposed to sh (POSIX or Bourne).
In sh, you'd have to do things manually:
out="${TMPDIR:-/tmp}/out.$$" err="${TMPDIR:-/tmp}/err.$$"
mkfifo "$out" "$err"
trap 'rm "$out" "$err"' EXIT
tee -a stdout.log < "$out" &
tee -a stderr.log < "$err" >&2 &
command >"$out" 2>"$err"
Simply:
./aaa.sh 2>&1 | tee -a log
This simply redirects standard error to standard output, so tee echoes both to log and to the screen. Maybe I'm missing something, because some of the other solutions seem really complicated.
Note: Since Bash version 4 you may use |& as an abbreviation for 2>&1 |:
./aaa.sh |& tee -a log
This may be useful for people finding this via Google. Simply uncomment the example you want to try out. Of course, feel free to rename the output files.
#!/bin/bash
STATUSFILE=x.out
LOGFILE=x.log
### All output to screen
### Do nothing, this is the default
### All Output to one file, nothing to the screen
#exec > ${LOGFILE} 2>&1
### All output to one file and all output to the screen
#exec > >(tee ${LOGFILE}) 2>&1
### All output to one file, STDOUT to the screen
#exec > >(tee -a ${LOGFILE}) 2> >(tee -a ${LOGFILE} >/dev/null)
### All output to one file, STDERR to the screen
### Note you need both of these lines for this to work
#exec 3>&1
#exec > >(tee -a ${LOGFILE} >/dev/null) 2> >(tee -a ${LOGFILE} >&3)
### STDOUT to STATUSFILE, stderr to LOGFILE, nothing to the screen
#exec > ${STATUSFILE} 2>${LOGFILE}
### STDOUT to STATUSFILE, stderr to LOGFILE and all output to the screen
#exec > >(tee ${STATUSFILE}) 2> >(tee ${LOGFILE} >&2)
### STDOUT to STATUSFILE and screen, STDERR to LOGFILE
#exec > >(tee ${STATUSFILE}) 2>${LOGFILE}
### STDOUT to STATUSFILE, STDERR to LOGFILE and screen
#exec > ${STATUSFILE} 2> >(tee ${LOGFILE} >&2)
echo "This is a test"
ls -l sdgshgswogswghthb_this_file_will_not_exist_so_we_get_output_to_stderr_aronkjegralhfaff
ls -l ${0}
In other words, you want to pipe stdout into one filter (tee bbb.out) and stderr into another filter (tee ccc.out). There is no standard way to pipe anything other than stdout into another command, but you can work around that by juggling file descriptors.
{ { ./aaa.sh | tee bbb.out; } 2>&1 1>&3 | tee ccc.out; } 3>&1 1>&2
See also How to grep standard error stream (stderr)? and When would you use an additional file descriptor?
In bash (and ksh and zsh), but not in other POSIX shells such as dash, you can use process substitution:
./aaa.sh > >(tee bbb.out) 2> >(tee ccc.out)
Beware that in bash, this command returns as soon as ./aaa.sh finishes, even if the tee commands are still executed (ksh and zsh do wait for the subprocesses). This may be a problem if you do something like ./aaa.sh > >(tee bbb.out) 2> >(tee ccc.out); process_logs bbb.out ccc.out. In that case, use file descriptor juggling or ksh/zsh instead.
To redirect standard error to a file, display standard output to the screen, and also save standard output to a file:
./aaa.sh 2>ccc.out | tee ./bbb.out
To display both standard error and standard output to screen and also save both to a file, you can use Bash's I/O redirection:
#!/bin/bash
# Create a new file descriptor 4, pointed at the file
# which will receive standard error.
exec 4<>ccc.out
# Also print the contents of this file to screen.
tail -f ccc.out &
# Run the command; tee standard output as normal, and send standard error
# to our file descriptor 4.
./aaa.sh 2>&4 | tee bbb.out
# Clean up: Close file descriptor 4 and kill tail -f.
exec 4>&-
kill %1
If using Bash:
# Redirect standard out and standard error separately
% cmd >stdout-redirect 2>stderr-redirect
# Redirect standard error and out together
% cmd >stdout-redirect 2>&1
# Merge standard error with standard out and pipe
% cmd 2>&1 |cmd2
Credit (not answering from the top of my head) goes here: Re: bash : stderr & more (pipe for stderr)
If you're using Z shell (zsh), you can use multiple redirections, so you don't even need tee:
./cmd 1>&1 2>&2 1>out_file 2>err_file
Here you're simply redirecting each stream to itself and the target file.
Full example
% (echo "out"; echo "err">/dev/stderr) 1>&1 2>&2 1>/tmp/out_file 2>/tmp/err_file
out
err
% cat /tmp/out_file
out
% cat /tmp/err_file
err
Note that this requires the MULTIOS option to be set (which is the default).
MULTIOS
Perform implicit tees or cats when multiple redirections are attempted (see Redirection).
Like the accepted answer well explained by lhunath, you can use
command > >(tee -a stdout.log) 2> >(tee -a stderr.log >&2)
Beware than if you use bash you could have some issue.
Let me take the matthew-wilcoxson example.
And for those who "seeing is believing", a quick test:
(echo "Test Out";>&2 echo "Test Err") > >(tee stdout.log) 2> >(tee stderr.log >&2)
Personally, when I try, I have this result:
user#computer:~$ (echo "Test Out";>&2 echo "Test Err") > >(tee stdout.log) 2> >(tee stderr.log >&2)
user#computer:~$ Test Out
Test Err
Both messages do not appear at the same level. Why does Test Out seem to be put like if it is my previous command?
The prompt is on a blank line letting me think the process is not finished, and when I press Enter this fix it.
When I check the content of the files, it is ok, and redirection works.
Let’s take another test.
function outerr() {
echo "out" # stdout
echo >&2 "err" # stderr
}
user#computer:~$ outerr
out
err
user#computer:~$ outerr >/dev/null
err
user#computer:~$ outerr 2>/dev/null
out
Trying again the redirection, but with this function:
function test_redirect() {
fout="stdout.log"
ferr="stderr.log"
echo "$ outerr"
(outerr) > >(tee "$fout") 2> >(tee "$ferr" >&2)
echo "# $fout content: "
cat "$fout"
echo "# $ferr content: "
cat "$ferr"
}
Personally, I have this result:
user#computer:~$ test_redirect
$ outerr
# stdout.log content:
out
out
err
# stderr.log content:
err
user#computer:~$
No prompt on a blank line, but I don't see normal output. The stdout.log content seem to be wrong, and only stderr.log seem to be ok.
If I relaunch it, the output can be different...
So, why?
Because, like explained here:
Beware that in bash, this command returns as soon as [first command] finishes, even if the tee commands are still executed (ksh and zsh do wait for the subprocesses)
So, if you use Bash, prefer use the better example given in this other answer:
{ { outerr | tee "$fout"; } 2>&1 1>&3 | tee "$ferr"; } 3>&1 1>&2
It will fix the previous issues.
Now, the question is, how to retrieve exit status code?
$? does not work.
I have no found better solution than switch on pipefail with set -o pipefail (set +o pipefail to switch off) and use ${PIPESTATUS[0]} like this:
function outerr() {
echo "out"
echo >&2 "err"
return 11
}
function test_outerr() {
local - # To preserve set option
! [[ -o pipefail ]] && set -o pipefail; # Or use second part directly
local fout="stdout.log"
local ferr="stderr.log"
echo "$ outerr"
{ { outerr | tee "$fout"; } 2>&1 1>&3 | tee "$ferr"; } 3>&1 1>&2
# First save the status or it will be lost
local status="${PIPESTATUS[0]}" # Save first, the second is 0, perhaps tee status code.
echo "==="
echo "# $fout content :"
echo "<==="
cat "$fout"
echo "===>"
echo "# $ferr content :"
echo "<==="
cat "$ferr"
echo "===>"
if (( status > 0 )); then
echo "Fail $status > 0"
return "$status" # or whatever
fi
}
user#computer:~$ test_outerr
$ outerr
err
out
===
# stdout.log content:
<===
out
===>
# stderr.log content:
<===
err
===>
Fail 11 > 0
In my case, a script was running command while redirecting both stdout and stderr to a file, something like:
cmd > log 2>&1
I needed to update it such that when there is a failure, take some actions based on the error messages. I could of course remove the dup 2>&1 and capture the stderr from the script, but then the error messages won't go into the log file for reference. While the accepted answer from lhunath is supposed to do the same, it redirects stdout and stderr to different files, which is not what I want, but it helped me to come up with the exact solution that I need:
(cmd 2> >(tee /dev/stderr)) > log
With the above, log will have a copy of both stdout and stderr and I can capture stderr from my script without having to worry about stdout.
The following will work for KornShell (ksh) where the process substitution is not available,
# create a combined (standard input and standard output) collector
exec 3 <> combined.log
# stream standard error instead of standard output to tee, while draining all standard output to the collector
./aaa.sh 2>&1 1>&3 | tee -a stderr.log 1>&3
# cleanup collector
exec 3>&-
The real trick here, is the sequence of the 2>&1 1>&3 which in our case redirects the standard error to standard output and redirects the standard output to file descriptor 3. At this point the standard error and standard output are not combined yet.
In effect, the standard error (as standard input) is passed to tee where it logs to stderr.log and also redirects to file descriptor 3.
And file descriptor 3 is logging it to combined.log all the time. So the combined.log contains both standard output and standard error.
Thanks lhunath for the answer in POSIX.
Here's a more complex situation I needed in POSIX with the proper fix:
# Start script main() function
# - We redirect standard output to file_out AND terminal
# - We redirect standard error to file_err, file_out AND terminal
# - Terminal and file_out have both standard output and standard error, while file_err only holds standard error
main() {
# my main function
}
log_path="/my_temp_dir"
pfout_fifo="${log_path:-/tmp}/pfout_fifo.$$"
pferr_fifo="${log_path:-/tmp}/pferr_fifo.$$"
mkfifo "$pfout_fifo" "$pferr_fifo"
trap 'rm "$pfout_fifo" "$pferr_fifo"' EXIT
tee -a "file_out" < "$pfout_fifo" &
tee -a "file_err" < "$pferr_fifo" >>"$pfout_fifo" &
main "$#" >"$pfout_fifo" 2>"$pferr_fifo"; exit
Compilation errors which are sent to standard error (STDERR) can be redirected or save to a file by:
Bash:
gcc temp.c &> error.log
C shell (csh):
% gcc temp.c |& tee error.log
See: How can I redirect compilation/build error to a file?