- Redirect all output to file in Bash [duplicate]
- 9 Answers 9
- How to redirect output to a file and stdout
- 11 Answers 11
- Can linux cat command be used for writing text to file?
- 14 Answers 14
- How to Write Data into File in Linux
- Write Data into File using CLI (Command Line Interface)
- How to Write Data to File Using cat Command
- How to Write Data to File Using echo command
- How to Write Data to File Using the printf Command
- Write data to a file using any nano text editor
- Write Data into File using Graphical User Interface
- Conclusion
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:
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 Can linux cat command be used for writing text to file?
This doesn’t work for me, but also doesn’t throw any errors. Specifically interested in a cat -based solution (not vim/vi/emacs, etc.). All examples online show cat used in conjunction with file inputs, not raw text.
14 Answers 14
echo "Some text here." > myfile.txt If you need to use double quotes in your text, encompass the whole thing in single quotes. This is useful for .json and the likes, e.g. echo ‘<"info1": "123456">‘ > info.json
Sounds like you’re looking for a Here document
cat > outfile.txt some text >to save >EOF The > characters represent the default value of $PS2 ; they show up automatically, and are not meant to be typed. If you have a different value for $PS2 , that will show up instead.
cat > outfile.txt >Enter text >to save press ctrl-d I use the following code to write raw text to files, to update my CPU-settings. Hope this helps out! Script:
#!/bin/sh cat > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor This writes the text "performance" to the two files mentioned in the script above. This example overwrite old data in files.
This code is saved as a file (cpu_update.sh) and to make it executable run:
After that, you can run the script with:
IF you do not want to overwrite the old data in the file, switch out
cat > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor cat >> /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor This will append your text to the end of the file without removing what other data already is in the file.
How to Write Data into File in Linux
Various Linux operating systems across the world provide several functionalities and writing data to file is one of them. The two most common operations with the file are read and write; in this article, we will discuss different ways to write data into the file on Ubuntu 20.04, which is the most popular and commonly used Linux distribution.
It is obvious that we need to store our data on the computer otherwise it gets lost, so we need to write data to a file, so it remains safe and stored. All operating systems provide ways to write data to a file. In Linux, we can also write data to files through the command line, bash scripting, and graphical user interface. If you are a new Linux user or want to learn how to write to a file in Linux, follow any of the procedures mentioned below according to your requirement
You need to first create the file in which you want to write, or the file should already exist in which you want to write.
Write Data into File using CLI (Command Line Interface)
One of the most common ways to perform functions in Linux is by writing commands in a terminal using the Command Line Interface. In this part, we will discuss how to write data to a file using the CLI using different approaches.
- Write data to a file using the “cat command.”
- Write data to a file using the “echo command.”
- Write data to a file using the “printf command.”
- Write data to file using any ” nano text editor.”
These approaches are discussed in detail below.
How to Write Data to File Using cat Command
The cat is preinstalled in new Ubuntu versions, but if you are using an older version, you will need to install it. It is used to create and write data in a text file efficiently. This will save you time by avoiding the need to open an editor, and this command is also simple. The below-mentioned command will create the “linux.txt” file if it doesn’t exist or open it to edit it if it is already present.
Two redirect symbols >> are used before the filename. A single redirect symbol > can also be used, but only if it will overwrite the content previously written in the file.
Press enter and now write the below-mentioned line in the file linux.txt.
This is linux 1
After writing the content you want to write in the file, press Ctrl+C to save the content in the file.
To check whether the content is inserted into the file “linux.txt” run the below-mentioned command:
$ cat linux.txt
How to Write Data to File Using echo command
The “echo” is like the cat command; however, it has a lot more flexibility. This command is typically used to print text to the terminal, but it can also be used to write to a file or create an empty file. It is a pre-installed command in almost all versions of Ubuntu, but if it is not installed, you need to install it.
The below-mentioned command will write the text into the linux.txt file:
$ echo 'This is linux 2' >> linux.txt
Now to check the insertion of text display the content of file “linux.txt” by below mentioned command:
$ cat linux.txt
How to Write Data to File Using the printf Command
This pre-installed command has the same functionality as that of the echo command except that it follows “C-style” rather than the Shell-Editing style. The below-mentioned command will write the text into the linux.txt file:
printf "This is linux3" >> linux.txt
Now to check the insertion of text display the content of file “linux.txt” by below mentioned command:
$ cat linux.txt
Write data to a file using any nano text editor
This is the slowest and most time-consuming way, although it can be helpful for Linux newcomers. The nano and other command-line text editors can be used to heavily modify a text file. It is preinstalled in new Ubuntu versions but if you are using an older version you need to install it.
The below-mentioned command will open the text file “linux.txt”:
$ nano linux.txt
Now enter the text you want to write in the file, then press “Ctrl+S” to save the file, “Ctrl+X” to exit, and press “Y” to confirm yes.
Write Data into File using Graphical User Interface
Linux also provides a way to insert text into a file using a graphical user interface in the same way we did in Windows.
Firstly, open the file in which you want to enter the text.
Now write the text into the opened file and then click on the “Save” button to save the text and then close the file.
Conclusion
Files can be used to perform various functions, such as creating, writing, editing, deleting, and saving. In this article, the function of writing data to a file is discussed in detail. There are two main approaches to writing data to file; command-line interface and graphical user interface. In CLI, we discussed how to write data through “cat”, “echo,” and “printf” commands, and through the “nano” text editor.
Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications including CCNA RS, SCP, and ACE. As an IT engineer and technical author, he writes for various websites.