Command Output Redirect to File and Terminal

Command output redirect to file and terminal

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

ls 2>&1 | tee /tmp/ls.txt

How to redirect output to a file and stdout

The command you want is named tee:

foo | tee output.file

For example, if you only care about stdout:

ls -a | tee output.file

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

redirect the output to terminal to a file in a batch file

Continuing from my comment, you have several options on how to redirect the output of your shell script calling mpirun and a.out to an output file.

1. the most common and rudimentary is simply to redirect the entire output of the shell script to the output file, e.g. bash scriptname.sh > output.txt;
2. the second option would be to redirect the output of the mpirun -np $i a.out command itself which would write to the output file 14 times in the example you show, e.g. mpirun -np $i a.out >> output.txt, note the >> redirection to append to the file (also, as noted you will want to truncate output.txt before the loop if you need to write to an empty file each time);
3. similar to 2. above you could execute the mpirun command in a subshell, which buys you little in your example, but is an option and helpful in certain circumstances; and
4. an optimal way of redirecting just the output produced by the loop within the shell script to output.txt is to use a brace-enclosed group to allow a single redirection of the entire output produced by the loop, e.g. { for ((...)); do ... done } > output.txt

For example, if your mpirun ... command produces output to stdout (similar to the simple example below)

#include <stdio.h>

int main (int argc, char **argv) {

    char *s = argc > 1 ? argv[1] : "default";

    printf ("%s\n", s);

    return 0;
}

(compiled as echoarg)

An example shell script mimicking your loop and using a brace-enclosed-group to redirect to output.txt could be written as:

#!/bin/bash

exefile="${1:-./bin/echoarg}"   ## executable to call
outfile="${2:-output.txt}"      ## output file name
:> "$outfile"                   ## truncate outfile

[ -x "$exefile" ] || {
    printf "error: file not executable '%s'\n" "$exefile"
    exit 1
}

## braced group encosing for loop redirected to outfile
{
for ((i = 1; i < 15; i++))
do
    ./bin/echoarg "$i"
done
} > "$outfile"

Example Use/Output/Resulting File

$ ./echoarg.sh ./bin/echoarg dat/outfile.txt

and

$ cat dat/outfile.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14

Look things over and let me know if you have further questions.

Redirect all output to file in Bash

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:

foo > allout.txt 2>&1

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

how to redirect terminal command output via execve to std::string in c++

A good alternative is to use the pstream header file instead of execve, which creates a child process.

thanks to this post:

https://stackoverflow.com/a/10702464/5133238

Instead of using exec i capture the output and print it using the ncurses printw method:

  // run a process and create a streambuf that reads its stdout and stderr
  redi::ipstream proc("echo hello", redi::pstreams::pstdout | redi::pstreams::pstderr);
  std::string line;
  // read child's stdout
  while (std::getline(proc.out(), line)) {
   // the output is captured line by line here
   // so that i can do what i want with it
    printw(line.c_str());
    printw("\n");
  }

  // if reading stdout stopped at EOF then reset the state:
  if (proc.eof() && proc.fail()) {
    proc.clear();
  }
  // read child's stderr
  while (std::getline(proc.err(), line)) {
   // error message is captured line by line here
   // so that i can do what i want with it.
    printw(line.c_str());
    printw("\n");
  }

pstreams here:
http://pstreams.sourceforge.net/

Redirect all output to file using Bash on Linux?

If the server is started on the same terminal, then it's the server's stderr that is presumably being written to the terminal and which you are not capturing.

The best way to capture everything would be to run:

script output.txt

before starting up either the server or the client. This will launch a new shell with all terminal output redirected out output.txt as well as the terminal. Then start the server from within that new shell, and then the client. Everything that you see on the screen (both your input and the output of everything writing to the terminal from within that shell) will be written to the file.

When you are done, type "exit" to exit the shell run by the script command.

How to redirect the output of the time command to a file in Linux?

Try

{ time sleep 1 ; } 2> time.txt

which combines the STDERR of "time" and your command into time.txt

Or use

{ time sleep 1 2> sleep.stderr ; } 2> time.txt

which puts STDERR from "sleep" into the file "sleep.stderr" and only STDERR from "time" goes into "time.txt"

How to output data to file but also suppress output on the terminal?

/dev/null is equivalent to writing to nothing. It has a file interface, but does not record anything. If you want to retrieve the data, write it to a file:

command > grep.txt 2>&1

Now grep.txt has all the data you were looking for. There will be no output printed to the terminal. You read redirects from left to right: stdout goes to file, stderr goes to wherever stdout is currently going. 2>&1 grep.txt would read as stderr goes to stdout (terminal), stdout goes to file, so you will see error output but normal output would go to the file.

How to redirect output to a file in C?

Online, it says that > redirects command output to a file, and I'm not sure exactly what "command output" means.

"command output" refers to the stdout (Standard Output) stream of the program.

_{Do note that some shell commands are not separate programs but are actually shell builtins, though they'll still support output redirection. On Windows, most shell commands (like dir and del) are built-ins whereas on Linux/BSD/etc most shell commands are separate programs (like ls and mkdir)}

If your program calls puts( "foobar" ); then running ./name from Bash will display "foobar" in your terminal emulator. But if you run ./name > file.txt then the "foobar" text will be written to file.txt and it will not be displayed in your terminal emulator.

Try it with the ls command, for example: ls -al > files.txt. This works on Windows too (dir /s > files.txt).

I'm redirecting the output from my name.c file to the outputFileName.ext file. Does command output mean stdout?

Yes.

If so, which C keyword would I use to write information to the outputFileName.ext file from name.c as stdout?

You don't. This is a shell/OS feature and is not part of C.

Can't redirect command output to file

There are two types of output stream stdout and stderr. It is probably coming out on the stderr stream. The > by itself will only capture the stdout.

Try executing with

<cmd> &> filename

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