Quite often I'll use the following construct to pipe output to a log file, keeping the output also on the display
./command 2>&1 | tee output.log
I'm trying to do something similar, but with using a here document:
./command << HEREDOC
params
HEREDOC 2>&1 | tee output.log
This doesn't work - is it possible to achieve this?
Sure.
./command <<HEREDOC 2>&1 | tee output.log
params
HEREDOC
The here-document doesn't begin until the next line. The rest of the command is parsed as normal.
An example with expr:
xargs expr << HEREDOC | tee output.log
10 + 11
HEREDOC
Related
I already know how to use tee with process substitution to send output to various commands, and stdout, eg
command0 | tee >(command1) >(command2)
With the above line, stdout will be composed of interleaved lines from command0, command1, and command2.
Is there a way to prevent tee from writing to stdout, without removing the output of any commands it pipes to? So for the example above, for stdout to only have output from command1 and command2?
Most answers relating to teeing without stdout are only writing directly to files, and recommend using something like this:
command0 | tee file1 file2 >/dev/null
But with process substitution, that would consume all output from the other commands too.
command0 | tee >(command1) >(command2) >/dev/null
Is there some way to tell tee not to print to stdout, or to only consume the output directly from tee?
Try this:
( command0 | tee >(command1 1>&3 ) | command2 ) 3>&1
It redirects the stdout of command1 to pipe 3, so that command2 sees only the original source. At end, you redirect pipe 3 to stdout again.
Use this to test it:
( echo test | tee >( sed 's/^/1 /' >&3 ) | sed 's/^/2 /' ) 3>&1
The output is unordered and in my case:
2 test
1 test
I have seen a comment and an answer that use an extra >, but don't really explain why it does what it does. It seems like it is redirecting output somewhere but all I can tell so far is that it does what I'm looking for. This works:
command0 | tee > >(command1) >(command2)
command0 | tee >(command1) > >(command2)
it appears not to matter where the extra > is, so long as it is before at least one of the arguments to tee. So this will not work:
command0 | tee >(command1) >(command2) >
Without knowing what this is called, and with no further leads, I can't explain further.
in bash when we want to read file we use the cat command
cat file.txt
but if we don't want to use whitespace , we can type:
{cat,file.txt}
Is there a way to redirect output without using the symbols > or < or &
i mean is there an equivalent to this command:
cat file.txt > /dev/null
and Thanks.
|tee (called pipe-T) - will redirect output(same as >) to file but also prints at the stdout:
cat file.txt|tee outfile.txt
|tee -a: will append output to file (same as >>) but also prints at the stdout:
cat file.txt|tee -a outfile.txt
I don't understand why you'd want to, but you could do:
eval {cat,input} "$(echo _/dev/null | tr _ '\076')"
Apart from tee You may use exec to redirect the output
exec 3>&1 # making file descriptor 3 to point to 1 where 1 is stdout
exec 1>fileout #redirecting 1 ie stdout to a file
{cat,file} # this goes to fileout & question requirement
exec 1>&3 # restoring 1 to default
{cat,38682813.c} # This will be printed at the stdout
I am trying to run the following command
./someprogram | tee /dev/tty | sed 's/^.\{2\}//' > output_file
But the file is always blank when I go to check it. If I remove > output_file from the end of the command, I am able to see the output from sed without any issues.
Is there any way that I can redirect the output from sed in this command to a file?
Remove output-buffering from sed command using the -u flag and make sure what you want to log isn't on stderr
-u, --unbuffered
load minimal amounts of data from the input files and flush the output buffers more often
Final command :
./someprogram | tee /dev/tty | sed -u 's/^.\{2\}//' > output_file
This happens with streams (usually a program sending output to stdout during its whole lifetime).
sed / grep and other commands do some buffering in those cases and you have to explicitly disable it to be able to have an output while the program is still running.
You got a Stderr & stdout problem. Checkout In the shell, what does " 2>&1 " mean? on this topic. Should fix you right up.
Construct the pipe to execute the following job.
"Output of ls should be displayed on the screen and from this output the lines
containing the word ‘poem’ should be counted and the count should be
stored in a file.”
If bash is allowed, use a process substitution as the receiver for tee
ls | tee >( grep -c poem > number.of.poetry.files)
Your attempt was close:
ls | tee /dev/tty | grep poem | wc -l >number_of_poems
The tee /dev/tty copies all ls output to the terminal. This satisfies the requirement that "Output of ls should be displayed on the screen." while also sending ls's output to grep's stdin.
This can be further simplified:
ls | tee /dev/tty | grep -c poem >number_of_poems
Note that neither of these solutions require bash. Both will work with lesser shells and, in particular, with dash which is the default /bin/sh under debian-like systems.
This sounds like a homework assignment :)
#!/bin/bash
ls
ls -l | grep -c poem >> file.txt
The first ls will display the output on the screen
The next line uses a series of pipes to output the number of files/directories containing "poem"
If there were 5 files with poem in them, file.txt would read 5. If file.txt already exists, the new count will be appended to the end. If you want overwrite file each time, change the line to read ls -l | grep -c poem > file.txt
I am writing a KornShell (ksh) script that is logging to a file. I am redirecting the output of one of my commands (scp) to the same file, but I would like to add a tab at the start of those lines in the log file if possible.
Is this possible to do?
EDIT: Also I should mention that the text I am redirecting is coming from stderr. My line currently looks like this:
scp -q ${wks}:${file_location} ${save_directory} >> ${script_log} 2>&1
Note: the below doesn't work for ksh (see this question for possible solutions).
You probably can do something like
my_command | sed 's/^/\t/' >> my.log
The idea is to process the output of the command with a stream editor like sed in some manner. In this case, a tab will be added at the beginning of every line. Consider:
$ echo -e 'Test\nfoobar' | sed 's/^/\t/'
Test
foobar
I haven't tested this in ksh, but a quick web search suggests that it should work.
Also note that some commands can write to both stdout and stderr, don't forget to handle it.
Edit: in response to the comment and the edit in the question, the adjusted command can look like
scp -q ${wks}:${file_location} ${save_directory} 2>&1 | \
sed 's/^/\t/' >> ${script_log}
or, if you want to get rid of stdout completely,
scp -q ${wks}:${file_location} ${save_directory} 2>&1 >/dev/null | \
sed 's/^/\t/' >> ${script_log}
The technique is described in this answer.