Linux output to file and terminal

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:

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Command output redirect to file and terminal [duplicate]

I am trying to throw command output to file plus console also. This is because i want to keep record of output in file. I am doing following and it appending to file but not printing ls output on terminal.

3 Answers 3

Yes, if you redirect the output, it won’t appear on the console. Use tee .

In this case error is merged into the output ( 2>&1 ), so the next process consuming the pipe will see both of them as regular input (in short: yes).

How to give the size of ls.txt file in above command so that it does not exceeds that given size. And once it exceeds max size, how to create a new file in that same directory (for eg: ls1.txt,ls2.txt. )

Be aware that you will loose the exit status of ls . If you want to retain the exit status of ls , or more precisely want to figure out if something in your pipe failed despite tee being the last (and very likely successful) command in your pipe, you need to use set -o pipefail .

It is worth mentioning that 2>&1 means that standard error will be redirected too, together with standard output. So

someCommand | tee someFile 

gives you just the standard output in the file, but not the standard error: standard error will appear in console only. To get standard error in the file too, you can use

someCommand 2>&1 | tee someFile 

(source: In the shell, what is » 2>&1 «? ). Finally, both the above commands will truncate the file and start clear. If you use a sequence of commands, you may want to get output&error of all of them, one after another. In this case you can use -a flag to «tee» command:

someCommand 2>&1 | tee -a someFile 

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How do I save terminal output to a file?

How do I save the output of a command to a file? Is there a way without using any software? I would like to know how.

10 Answers 10

Yes it is possible, just redirect the output (AKA stdout ) to a file:

Or if you want to append data:

If you want stderr as well use this:

if you want to have both stderr and output displayed on the console and in a file use this:

SomeCommand 2>&1 | tee SomeFile.txt 

(If you want the output only, drop the 2 above)

Note that someCommand 2> someFile.txt and someCommand 2>> someFile.txt also redirects stterr to someFile.txt

I’m trying to do this with gcc command but it doesn’t work. It works with other commands, but not this one. It simply creates the output file with nothing inside it.

@Nik-Lz Often this is because the command is sending all its output on stderr. If gcc is generating error messages, this seems likely. See Slothworks comment for how to capture stderr instead of stdout.

NB: to get the output of the make command into a file it requires this syntax instead: make > someFile.txt 2>&1 (source: linuxquestions.org/questions/linux-newbie-8/…)

To write the output of a command to a file, there are basically 10 commonly used ways.

Overview:

_{Please note that the n.e. in the syntax column means «not existing».
There is a way, but it’s too complicated to fit into the column. You can find a helpful link in the List section about it.}

 || visible in terminal || visible in file || existing Syntax || StdOut | StdErr || StdOut | StdErr || file ==========++==========+==========++==========+==========++=========== > || no | yes || yes | no || overwrite >> || no | yes || yes | no || append || | || | || 2> || yes | no || no | yes || overwrite 2>> || yes | no || no | yes || append || | || | || &> || no | no || yes | yes || overwrite &>> || no | no || yes | yes || append || | || | || | tee || yes | yes || yes | no || overwrite | tee -a || yes | yes || yes | no || append || | || | || n.e. (*) || yes | yes || no | yes || overwrite n.e. (*) || yes | yes || no | yes || append || | || | || |& tee || yes | yes || yes | yes || overwrite |& tee -a || yes | yes || yes | yes || append 

List:

• command > output.txt The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.
• command >> output.txt The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.
• command 2> output.txt The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.
• command 2>> output.txt The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.
• command &> output.txt Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, it gets overwritten.
• command &>> output.txt Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, the new data will get appended to the end of the file..
• command | tee output.txt The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, it gets overwritten.
• command | tee -a output.txt The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.
• (*) Bash has no shorthand syntax that allows piping only StdErr to a second command, which would be needed here in combination with tee again to complete the table. If you really need something like that, please look at «How to pipe stderr, and not stdout?» on Stack Overflow for some ways how this can be done e.g. by swapping streams or using process substitution.
• command |& tee output.txt Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, it gets overwritten.
• command |& tee -a output.txt Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

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How to Save Command Output to a File in Linux

Linux command line interface (CLI) is a powerful tool that allows users to interact with the operating system using text-based commands. One common task in the CLI is executing commands and capturing their output to a file for later use. In this article, we’ll explore various ways to save command output to a file in Linux.

Understanding Output Streams

Before we dive into the different ways to save command output, it’s important to understand how output streams work in Linux. There are three main types of output streams:

• Standard Output (stdout): Standard Output is the default output stream where a command sends its output. By default, stdout sends output to the terminal window.
• Standard Error (stderr): Standard Error outputs error messages or diagnostics. Like stdout, stderr also sends its output to the terminal window.
• Standard Input (stdin): Standard Input accepts input from the user. Unlike stdout and stderr, stdin is not visible in the terminal window.

Saving Command Output to a File

Now that we understand the different output streams let’s explore how to save command output to a file in Linux.

Saving Standard Output to a File

To save the standard output of a command to a file, we can use the “>” (redirect) operator followed by the filename. For example, the following command will save the output of the “ls” command to a file named “filelist.txt”:

If the file “filelist.txt” already exists, its contents will be overwritten. To append the output to the end of an existing file, we can use the “>>” (append) operator instead of the “>” operator:

Saving Standard Error to a File

To save the standard error of a command to a file, we can use the “2>” (redirect standard error) operator followed by the filename. For example, the following command will save any error messages produced by the “ls” command to a file named “errorlog.txt”:

ls /invalid/path 2> errorlog.txt

The file “errorlog.txt” will be empty if there are no errors.

Saving Both Standard Output and Standard Error to a File

To save both the standard output and standard error of a command to a file, we can use the “&>” (redirect both stdout and stderr) operator followed by the filename. For example, the following command will save both the output and any error messages produced by the “ls” command to a file named “output.txt”:

ls /invalid/path &> output.txt

Using Pipes to Save Output to a File

In addition to the above methods, we can also use pipes to save the output of a command to a file. A pipe is a way to redirect the output of one command as input to another command. To save the output of a command to a file using a pipe, we can use the “|” (pipe) operator followed by the “tee” command and the filename. For example, the following command will save the output of the “ls” command to a file named “filelist.txt” using the “tee” command:

The “tee” command displays the output on the terminal window and saves it to the file.

Using xargs to Save Output to a File

Another useful tool to save command output to a file is xargs. xargs is a command that reads items from standard input and executes a command for each item. To save the command output to a file using xargs, we can use the “>” (redirect) operator followed by the filename, as shown below:

echo "file1.txt file2.txt file3.txt" | xargs cat > combined.txt 

The above command will concatenate the contents of the files file1.txt, file2.txt, and file3.txt and save the output to a file named combined.txt.

Saving Command Output to Multiple Files

Sometimes, we may want to save the output of a command to multiple files. We can achieve this by using brace expansion in the command. For example, the following command will save the output of the “ls” command to files named “file1.txt”, “file2.txt”, and “file3.txt”:

Conclusion

Once you understand the different output streams and redirection operators, saving command output to a file in Linux is a simple task. Using these methods, you can easily save the output of a command to a file for later use. Always refer to the official documentation and community resources for more information and help with Linux commands.

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