Writing outputs to log file and console

Question

In Unix shell  I have a env file  env file defines the parameters required for running the user script like log file name and path  redirect outputs and errors to log file  database connection details  etc  which redirects all the outputs  echo messages  and errors to the log file from the executed script using the following code   exec 1 gt  gt   LOG FILE  exec 2 gt  gt   LOG FILE    The env file is executed at the beginning of each script  Due to the above code in env file all the console outputs that might be user outputs or errors are directly output to the log file which is what I actually needed   But there are some selective user outputs which I want to be displayed in both the console and the log file  But because of the above code I am not able to do so   I know that if I remove the above code I can get the desired result for this case  but I will have to manually write all other outputs to the log file which is not an easy task   Is there a way to get the output in both the console and the log file without removing the above codes

User · Answer

I have found a way to get the desired output. Though it may be somewhat unorthodox way. Anyways here it goes. In the redir.env file I have following code:

#####redir.env#####    
export LOG_FILE=log.txt

      exec 2>>${LOG_FILE}

    function log {
     echo "$1">>${LOG_FILE}
    }

    function message {
     echo "$1"
     echo "$1">>${LOG_FILE}
    }

Then in the actual script I have the following codes:

#!/bin/sh 
. redir.env
echo "Echoed to console only"
log "Written to log file only"
message "To console and log"
echo "This is stderr. Written to log file only" 1>&2

Here echo outputs only to console, log outputs to only log file and message outputs to both the log file and console.

After executing the above script file I have following outputs:

In console

In console
Echoed to console only
To console and log

For the Log file

In Log File Written to log file only
This is stderr. Written to log file only
To console and log

Hope this help.

User · Answer

I wanted to display logs on stdout and log file along with the timestamp  None of the above answers worked for me   I made use of process substitution and exec command and came up with the following code  Sample logs    2017-06-21 11 16 41 05 30 Fetching information about files in the directory      Add following lines at the top of your script    LOG FILE script log exec  gt   gt  while read -r line  do printf   s  s n     date --rfc-3339 seconds     line    tee -a  LOG FILE  done  exec 2 gt   gt  while read -r line  do printf   s  s n     date --rfc-3339 seconds     line    tee -a  LOG FILE  done  gt  amp 2    Hope this helps somebody

User · Answer

Yes  you want to use tee      tee - read from standard input and write to standard output and files   Just pipe your command to tee and pass the file as an argument  like so   exec 1   tee   LOG FILE  exec 2   tee   LOG FILE    This both prints the output to the STDOUT and writes the same output to a log file  See man tee for more information   Note that this won t write stderr to the log file  so if you want to combine the two streams then use   exec 1 2 gt  amp 1   tee   LOG FILE

User · Answer

I find it very useful to append both stdout and stderr to a log file  I was glad to see a solution by alfonx with exec  gt   gt  tee -a   because I was wondering how to accomplish this using exec  I came across a creative solution using here-doc syntax and    https   unix stackexchange com questions 80707 how-to-output-text-to-both-screen-and-file-inside-a-shell-script  I discovered that in zsh  the here-doc solution can be modified using the  multios  construct to copy output to both stdout stderr and the log file      bin zsh LOG  0 log   8 is an arbitrary number    multiple redirects for the same file descriptor    triggers  multios    8 lt  lt  EOF  dev fd 8 2 gt  amp 2  gt  amp 1 2 gt  gt  LOG  gt  gt  LOG   some commands date  gt  amp 2 set -x echo hi echo bye EOF echo not logged   It is not as readable as the exec solution but it has the advantage of allowing you to log just part of the script  Of course  if you omit the EOF then the whole script is executed with logging  I m not sure how zsh implements multios  but it may have less overhead than tee  Unfortunately it seems that one cannot use multios with exec

User · Answer

for log file you may date to enter into text data  following code may help    declaring variables  Logfile  logfile txt     MAIL LOG  Message to print in log file    Location  were is u want to store log file   cd  Location    if   -f  Logfile     then    echo   MAIL LOG    gt  gt   Logfile  else          touch  Logfile    echo   MAIL LOG   gt  gt   Logfile      fi     ouput  2    Log file will be created in first run and keep on updating from next runs  In case log file missing in future run   script will create new log file

User · Answer

exec 3 gt  amp 1 1 gt  gt   LOG FILE  2 gt  amp 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 gt  amp 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 gt  amp 1 1 gt  gt   LOG FILE  2 gt  amp 1  echo  This is stdout  echo  This is stderr  1 gt  amp 2 echo  This is the console  fd 3   1 gt  amp 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

User · Answer

Try this  it will do the work   log file  curr dir log file txt exec  gt   gt  tee -a   log file    exec 2 gt   gt  tee -a   log file   gt  amp 2

User · Answer

------------------------------------------------------------------------------       echo pass params and print them to a log file and terminal       with timestamp and  host name and  0 PID       usage        doLog  INFO some info message        doLog  DEBUG some debug message        doLog  WARN some warning message        doLog  ERROR some really ERROR message        doLog  FATAL some really fatal message       ------------------------------------------------------------------------------     doLog            type of msg   echo    cut -d    -f1          msg   echo      cut -d    -f2-              type of msg    DEBUG     amp  amp      do print debug msgs -ne 1     amp  amp  return             type of msg    INFO     amp  amp  type of msg  INFO     one space for aligning             type of msg    WARN     amp  amp  type of msg  WARN     as well            print to the terminal if we have one         test -t 1  amp  amp  echo     type of msg   date    Y  m  d- H  M  S  Z     run unit    host name          msg             define default log file none specified in cnf file         test -z  log file  amp  amp                mkdir -p  product instance dir dat log bash  amp  amp                    log file   product instance dir dat log bash  run unit  date    Y m   log          echo     type of msg   date    Y  m  d- H  M  S  Z     run unit    host name          msg   gt  gt   log file            eof func doLog

User · Answer

I tried joonty s answer  but I also got the      exec  1  not found   error  This is what works best for me  confirmed to work in zsh also       bin bash LOG FILE  tmp both log exec  gt   gt  tee   LOG FILE   2 gt  amp 1 echo  this is stdout  chmmm 77  makeError   The file  tmp both log afterwards contains  this is stdout chmmm command not found    The  tmp both log is appended unless you remove the -a from tee   Hint   gt       is a process substitution  It lets the exec to the tee command as if it were a file

[bash] Writing outputs to log file and console

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