Linux Append Console Output to a Logfile

Linux append console output to a logfile?

You can use >> for appending to the same logfile
for e.g cmd1 >> logfile.log
then use for other commnad like

cmd2 >> logfile.log

>> is used for append data to the file

Writing outputs to log file and console

exec 3>&1 1>>${LOG_FILE} 2>&1

would send stdout and stderr output into the log file, but would also leave you with fd 3 connected to the console, so you can do

echo "Some console message" 1>&3

to write a message just to the console, or

echo "Some console and log file message" | tee /dev/fd/3

to write a message to both the console and the log file - tee sends its output to both its own fd 1 (which here is the LOG_FILE) and the file you told it to write to (which here is fd 3, i.e. the console).

Example:

exec 3>&1 1>>${LOG_FILE} 2>&1

echo "This is stdout"
echo "This is stderr" 1>&2
echo "This is the console (fd 3)" 1>&3
echo "This is both the log and the console" | tee /dev/fd/3

would print

This is the console (fd 3)
This is both the log and the console

on the console and put

This is stdout
This is stderr
This is both the log and the console

into the log file.

How to show error on console while logging it to both log file and console in bash

If I understand well you'd like to send stderr to the console and to the log file, stdout only to the log file, plus be able to send messages both to the log file and the console with echo ... | tee /dev/fd/3.

To send stderr to the console and to the log file simply redirect it to a tee -a "$LOG_FILE" command using process substitution. Then make a copy of stdout to fd3 and redirect (append) stdout to the log file:

#!/usr/bin/env bash

LOG_FILE='./test1.log'
exec 2> >( tee -a "$LOG_FILE" ) 3>&1 1>>"$LOG_FILE"

echo "log to console and log file" | tee /dev/fd/3
echo "only to log file"
chmm 777 ${LOG_FILE}

Demo:

$ ./log_to_console_and_file.sh
log to console and log file
./log_to_console_and_file.sh: line 8: chmm: command not found
$ cat test1.log 
log to console and log file
only to log file
./log_to_console_and_file.sh: line 8: chmm: command not found

Of course you know already that the order of redirections matters.

Note that your shebang (!/bin/bash) is incorrect. Note also that as stderr now appends to console and log file you don't really need fd3 any more. To send something to console and log file you could probably simply redirect it to stderr...

How to redirect and append both standard output and standard error to a file with Bash

cmd >>file.txt 2>&1

Bash executes the redirects from left to right as follows:

1. >>file.txt: Open file.txt in append mode and redirect stdout there.
2. 2>&1: Redirect stderr to "where stdout is currently going". In this case, that is a file opened in append mode. In other words, the &1 reuses the file descriptor which stdout currently uses.

Redirect echo output in shell script to logfile

You can add this line on top of your script:

#!/bin/bash
# redirect stdout/stderr to a file
exec >logfile.txt 2>&1

OR else to redirect only stdout use:

exec > logfile.txt

output of shell script to console and file

You can use process substitution with exec builtin:

exec > >(tee trace.log) 2>&1

to redirect both stdout and stderr to a file as as well as show it in terminal.

How can I redirect console output to file?

Use shell output redirection

your-command > outputfile.txt

The standard error will still be output to the console. If you don't want that, use:

your-command > outputfile.txt 2>&1

or

your-command &> outputfile.txt

You should also look into the tee utility, which can make it redirect to two places at once.

Linux Script to redirect output to log file with date filename

You can use date to choose the format of the log file. Assuming YYYY-MM-DD, you can use the following. Note using '>>' to append/create the log file.

java abc.java >> "logfile.$(date +'%Y-%m-%d').log"
# Test
echo abc.java >> "logfile.$(date +'%Y-%m-%d').log"

Also note that 'java abc.java' need to be reviewed. The java command is usually invoked with class name (java abc), and not the name of a file.

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