Linux result to file

How to pipe the output of a command to file on Linux

I am running a task on the CLI, which prompts me for a yes/no input. After selecting a choice, a large amount of info scrolls by on the screen — including several errors. I want to pipe this output to a file so I can see the errors. A simple ‘>’ is not working since the command expects keyboard input. I am running on Ubuntu 9.1.

5 Answers 5

You can use &> to redirect both stdout and stderr to a file. This is shorthand for command > output.txt 2>&1 where the 2>&1 means «send stderr to the same place as stdout» (stdout is file descriptor 1, stderr is 2).

For interactive commands I usually don’t bother saving to a file if I can use less and read the results right away:

Redirecting both stdout and stderr to a file means he wont see the actual prompt. I can’t see how he would be any better off than the situation he describes in his question.

You used & at both side of the numbers ( 1 , 2 ). Is using &2 or 2& , even 2&>1 or 2>&1 makes any difference?

When the question arises: what is the meaining of & sign with a number after it (i.e. 2>&1) and without a number (you say without a number is both stdout and stderr, right)?

(1) If you write >2 then bash will write to a file named 2 . Writing >&2 tells bash that 2 is a file descriptor number instead of a file name. (2) Writing a number before the > does not require & , since a file name is never valid on the left. (3) &> is a special syntax for redirecting both stdout and stderr. It can also be written as >& , though &> is preferred. Both of these are special syntax. Don’t try to figure out what the > and & mean on their own. Think of &> as a single operator.

Источник

Redirect all output to file in Bash [duplicate]

I know that in Linux, to redirect output from the screen to a file, I can either use the > or tee . However, I’m not sure why part of the output is still output to the screen and not written to the file. Is there a way to redirect all output to file?

9 Answers 9

That part is written to stderr, use 2> to redirect it. For example:

foo > stdout.txt 2> stderr.txt 

or if you want in same file:

Note: this works in (ba)sh, check your shell for proper syntax

well, i found the reference and have deleted my post for having incorrect information. from the bash manual: ‘»ls 2>&1 > dirlist» directs only the standard output to dirlist, because the standard error was duplicated from the standard output before the standard output was redirected to dirlist» 🙂

also from the bash man «There are two formats for redirecting standard output and standard error: &>word and >&word Of the two forms, the first is preferred. This is semantically equivalent to >word 2>&1»

Two important addenda: If you want to pipe both stdout and stderr, you have to write the redirections in the opposite order from what works for files, cmd1 2>&1 | cmd2 ; putting the 2>&1 after the | will redirect stderr for cmd2 instead. If both stdout and stderr are redirected, a program can still access the terminal (if any) by opening /dev/tty ; this is normally done only for password prompts (e.g. by ssh ). If you need to redirect that too, the shell cannot help you, but expect can.

All POSIX operating systems have 3 streams: stdin, stdout, and stderr. stdin is the input, which can accept the stdout or stderr. stdout is the primary output, which is redirected with > , >> , or | . stderr is the error output, which is handled separately so that any exceptions do not get passed to a command or written to a file that it might break; normally, this is sent to a log of some kind, or dumped directly, even when the stdout is redirected. To redirect both to the same place, use:

EDIT: thanks to Zack for pointing out that the above solution is not portable—use instead:

If you want to silence the error, do:

Источник

How to redirect output to a file and stdout

In bash, calling foo would display any output from that command on the stdout. Calling foo > output would redirect any output from that command to the file specified (in this case ‘output’). Is there a way to redirect output to a file and have it display on stdout?

If someone just ended up here looking for capturing error output to file, take a look at — unix.stackexchange.com/questions/132511/…

A note on terminology: when you execute foo > output the data is written to stdout and stdout is the file named output . That is, writing to the file is writing to stdout. You are asking if it is possible to write both to stdout and to the terminal.

@WilliamPursell I’m not sure your clarification improves things 🙂 How about this: OP is asking if it’s possible to direct the called program’s stdout to both a file and the calling program’s stdout (the latter being the stdout that the called program would inherit if nothing special were done; i.e. the terminal, if the calling program is an interactive bash session). And maybe they also want to direct the called program’s stderr similarly («any output from that command» might be reasonably interpreted to mean including stderr).

If we have multiple commands that want to pipe outputs, use ( ) . For example (echo hello; echo world) | tee output.txt

11 Answers 11

The command you want is named tee :

For example, if you only care about stdout:

If you want to include stderr, do:

program [arguments. ] 2>&1 | tee outfile 

2>&1 redirects channel 2 (stderr/standard error) into channel 1 (stdout/standard output), such that both is written as stdout. It is also directed to the given output file as of the tee command.

Furthermore, if you want to append to the log file, use tee -a as:

program [arguments. ] 2>&1 | tee -a outfile 

If OP wants «all output» to be redirected, you’ll also need to grab stderr: «ls -lR / 2>&1 | tee output.file»

@evanmcdonnal The answer is not wrong, it just may not be specific enough, or complete depending on your requirements. There certainly are conditions where you might not want stderr as part of the output being saved to a file. When I answered this 5 years ago I assumed that the OP only wanted stdout, since he mentioned stdout in the subject of the post.

Ah sorry, I might have been a little confused. When I tried it I just got no output, perhaps it was all going to stderr.

Use -a argument on tee to append content to output.file , instead of overwriting it: ls -lR / | tee -a output.file

If you’re using $? afterwards it will return the status code of tee , which is probably not what you want. Instead, you can use $ .

$ program [arguments. ] 2>&1 | tee outfile 

2>&1 dumps the stderr and stdout streams. tee outfile takes the stream it gets and writes it to the screen and to the file «outfile».

This is probably what most people are looking for. The likely situation is some program or script is working hard for a long time and producing a lot of output. The user wants to check it periodically for progress, but also wants the output written to a file.

The problem (especially when mixing stdout and stderr streams) is that there is reliance on the streams being flushed by the program. If, for example, all the writes to stdout are not flushed, but all the writes to stderr are flushed, then they’ll end up out of chronological order in the output file and on the screen.

It’s also bad if the program only outputs 1 or 2 lines every few minutes to report progress. In such a case, if the output was not flushed by the program, the user wouldn’t even see any output on the screen for hours, because none of it would get pushed through the pipe for hours.

Update: The program unbuffer , part of the expect package, will solve the buffering problem. This will cause stdout and stderr to write to the screen and file immediately and keep them in sync when being combined and redirected to tee . E.g.:

$ unbuffer program [arguments. ] 2>&1 | tee outfile 

Источник

How to Save the Output of a Command to a File in Linux Terminal

When you run a command or script in the Linux terminal, it prints the output on the screen for your immediate viewing. What if you want to save it to a file?

When you run a command or script in the Linux terminal, it prints the output on the screen for your immediate viewing. There will be times when you need to save the output to a file for future references. Now, you can surely copy and paste in Linux terminal but there are better ways to save the output of a shell script or command in Linux command line. Let me show them to you.

Method 1: Use redirection to save command output to file in Linux

• The > redirects the command output to a file replacing any existing content on the file.
• The >> redirect adds the command output at the end of the file’s existing content (if any).

Use the STDOUT redirection operator > for redirecting the output to a file like this:

If the file.txt doesn’t exist, it will be created automatically. If you use the > redirect again with the same file, the file content is replaced by the new output.

The example below demonstrates it better. It first saves the output of ls -l command. And then later, it replaces the content of the file with the output of ls *.c command.

If you don’t want to lose the content of the existing file while saving the output of a script or command, use the redirection operation in append mode with >>.

This example demonstrates it better:

Even here, if the file doesn’t exist, it is created automatically.

Bonus Tip: Save Linux command output as well as error to a file

If your Linux command returns an error, it doesn’t get saved in the file. You can save both the command output and command error in the same file using 2>&1 like this:

Basically, 0 stands for standard input, 1 for standard output and 2 for standard error.

Here, you are redirecting (>) standard error (2) to the same address (&) as standard output (1).

Method 2: Use tee command to display the output and save it to a file as well

By the way, did you notice that when you send the command output to a file, you cannot see it anymore on the display? The tee command in Linux solves this problem for you.

Like a tee pipe that sends a water stream in two directions, the tee command sends the output to the display as well as to a file (or as input to another command). You can use it like this:

Again, the file will be created automatically if it doesn’t exist already.

You may also use the tee command in append mode with option -a in this manner:

Let me demonstrate it with some easy-to-follow examples:

I have used simple Linux commands in my examples. But rest assured; you can use these methods to save the output of bash scripts as well.

Note: Avoid pipe pitfall while saving command output to a file

You probably are familiar with pipe redirection. You may use it to combine Linux commands but you cannot pipe the output to a file. It will result in an error that filename command not found:

This is because the pipe redirects one command’s output to another command’s input. And in this case, you give it a file name while it is expecting a command.

If you are new to the Linux command line, I hope this quick tutorial added to your Linux knowledge a bit. I/O redirection is an essential concept that one should be aware of.

As always, questions and suggestions are always welcome.

Источник