Redirect stdout and stderr to Function
Based on the previous answers, I put together some generic functions that work with or without a log file, as listed at the end of this post. These are handy for more complex scripts. I generally print terminal window messages to stderr
so as to not interfere with legitimate program output that may need to be redirected. The functions can be called as follows:
scriptFolder=$(cd $(dirname "$0") && pwd)
scriptName=$(basename $scriptFolder)
# Start a log file that will be used by the logging functions
logFileStart ${scriptName} "${scriptFolder)/${scriptName}.log"
# The following logs the message string passed to the function.
# - use a space for empty lines because otherwise the logging function
# will hang waiting for input
logInfo " "
logInfo "Starting to do some work."
# The following will log each 'stdout` and `stderr` line piped to the function.
someOtherProgram 2>&1 | logInfo
Functions...
# Echo to stderr
echoStderr() {
# - if necessary, quote the string to be printed
# - redirect stdout from echo to stderr
echo "$@" 1>&2
# Or, use an alternate echo such one that colors textT
# ${echo2} "$@" 1>&2
}
# Print a DEBUG message
# - prints to stderr and optionally appends to log file if ${logFile} is defined globally
# - see logFileStart() to start a log file
# - call with parameters or pipe stdout and stderr to this function: 2>&1 | logDebug
# - print empty lines with a space " " to avoid hanging the program waiting on stdin input
logDebug() {
if [ -n "${1}" ]; then
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[DEBUG] $@" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[DEBUG] $@"
fi
else
while read inputLine; do
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[DEBUG] ${inputLine}" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[DEBUG] ${inputLine}"
fi
done
fi
}
# Print an ERROR message
# - prints to stderr and optionally appends to log file if ${logFile} is defined globally
# - see logFileStart() to start a log file
# - call with parameters or pipe stdout and stderr to this function: 2>&1 | logError
# - print empty lines with a space " " to avoid hanging the program waiting on stdin input
logError() {
if [ -n "${1}" ]; then
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[ERROR] $@" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[ERROR] $@"
fi
else
while read inputLine; do
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[ERROR] ${inputLine}" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[ERROR] ${inputLine}"
fi
done
fi
}
# Start a new logfile
# - name of program that is being run is the first argument
# - path to the logfile is the second argument
# - echo a line to the log file to (re)start
# - subsequent writes to the file using log*() functions will append
# - the global variable ${logFile} will be set for use by log*() functions
logFileStart() {
local newLogFile now programBeingLogged
programBeingLogged=$1
# Set the global logfile, in case it was not saved
if [ -n "${2}" ]; then
logFile=${2}
else
# Set the logFile to stderr if not specified, so it is handled somehow
logFile=/dev/stderr
fi
now=$(date '+%Y-%m-%d %H:%M:%S')
# Can't use logInfo because it only appends and want to restart the file
echo "Log file for ${programBeingLogged} started at ${now}" > ${logFile}
}
# Print an INFO message
# - prints to stderr and optionally appends to log file if ${logFile} is defined globally
# - see logFileStart() to start a log file
# - call with parameters or pipe stdout and stderr to this function: 2>&1 | logInfo
# - print empty lines with a space " " to avoid hanging the program waiting on stdin input
logInfo() {
if [ -n "${1}" ]; then
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[INFO] $@" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[INFO] $@"
fi
else
while read inputLine; do
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[INFO] ${inputLine}" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[INFO] ${inputLine}"
fi
done
fi
}
# Print an WARNING message
# - prints to stderr and optionally appends to log file if ${logFile} is defined globally
# - see logFileStart() to start a log file
# - call with parameters or pipe stdout and stderr to this function: 2>&1 | logWarning
# - print empty lines with a space " " to avoid hanging the program waiting on stdin input
logWarning() {
if [ -n "${1}" ]; then
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[WARNING] $@" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[WARNING] $@"
fi
else
while read inputLine; do
if [ -n "${logFile}" ]; then
# Are using a log file
echoStderr "[WARNING] ${inputLine}" 2>&1 | tee --append $logFile
else
# Are NOT using a log file
echoStderr "[WARNING] ${inputLine}"
fi
done
fi
}
To do this you can use the read
bash builtin:
LogMsg()
{
read IN # This reads a string from stdin and stores it in a variable called IN
DateTime=`date "+%Y/%m/%d %H:%M:%S"`
echo '*****'$DateTime' ('$QMAKESPEC'): '$IN >> "$LogFile"
echo $DateTime' ('$QMAKESPEC'): '$IN
}
And then use a pipe:
make 2>&1 | LogMsg
Update:
To be able to use stdin OR an argument as input (as per chepner's comment) you can do this:
LogMsg()
{
if [ -n "$1" ]
then
IN="$1"
else
read IN # This reads a string from stdin and stores it in a variable called IN
fi
DateTime=`date "+%Y/%m/%d %H:%M:%S"`
echo '*****'$DateTime' ('$QMAKESPEC'): '$IN >> "$LogFile"
echo $DateTime' ('$QMAKESPEC'): '$IN
}
It's an old thread.. but I have used it to help me write a log function that will output also multiple lines of a command output:
# Defines function to grab a time stamp #
get_Time () { Time=$(date +%Y-%m-%d\ %H:%M:%S) ; }
write_Log()
{
get_Time
if [ -n "${1}" ]; then # If it's from a "<message>" then set it
IN="${1}"
echo "${Time} ${IN}" | tee -a ${log_File}
else
while read IN # If it is output from command then loop it
do
echo "${Time} ${IN}" | tee -a ${log_File}
done
fi
}