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#!/bin/bash
# Script version global variable. Edit this whenever changes are made.
__ADVANCED_BASH_VERSION__="step_02"
# =======================================================================
# Helper functions
# =======================================================================
# Echo's its arguments to std error
echo_se() { echo "$@" 1>&2; }
# Sets up auto-logging to a log file in the current directory
# using the specified logFileTag (arg 1) in the log file name.
auto_log() {
local logFileTag="$1"
if [[ "$logFileTag" != "" ]]; then
local logFilePath="./autoLog_${logFileTag}.log"
echo_se ".. logging to $logFilePath"
exec 1> >(tee "$logFilePath") 2>&1
else
echo_se "** ERROR in auto_log: no logFile argument provided"
exit 255
fi
}
# =======================================================================
# Command processing functions
# =======================================================================
# function that says "Hello World!" and displays user-specified text.
function helloWorld() {
local txt1=$1
local txt2=$2
shift; shift
local rest=$@
echo "Hello World!"
echo " text 1: '$txt1'"
echo " text 2: '$txt2'"
echo " rest: '$rest'"
}
# function that displays its 1st argument on standard output and
# its 2nd argument on standard error
function stdStreams() {
local outTxt=${1:-"text for standard output"}
local errTxt=${2:-"text for standard error"}
echo "to standard output: '$outTxt'"
echo_se "to standard error: '$errTxt'"
}
# function that illustrates auto-logging and capturing function output
# arg 1 - (required) tag to identify the logfile
# arg 2 - (optional) text for standard output
# arg 3 - (optional) text for standard error
function testAutolog() {
local logFileTag="$1"
local outTxt=${2:-"text for standard output"}
local errTxt=${3:-"text for standard error"}
auto_log "$logFileTag"
echo -e "\n1) Call stdStreams with output and error text:"
stdStreams "$outTxt" "$errTxt"
echo -e "\n2) Capture echo output in a variable and display it:"
local output=`echo $outTxt`
echo -e " echo output was:\n$output"
echo -e "\n3) Call echo_se with error text:"
echo_se "$errTxt"
echo -e "\n4)Capture echo_se function output in a variable and display it:"
output=`echo_se "$errTxt"`
echo -e "echo_se output was: '$output'"
}
# =======================================================================
# Main script command-line processing
# =======================================================================
function usage() {
echo "
advanced_bash.sh, version $__ADVANCED_BASH_VERSION__
Usage: advanced_bash.sh <command> [arg1 arg2...]
Commands:
helloWorld [text to display]
stdStreams [text for stdout] [text for stderr]
testAutolog <logFileTag> [text for stdout] [text for stderr]
"
exit 255
}
CMD=$1 # initially $1 will be the command
shift # after "shift", $1 will be the 2nd command-line argument; $2 the 3rd, etc.
# and $@ will be arguments 2, 3, etc.
case "$CMD" in
helloWorld) helloWorld "$@"
;;
stdStreams) stdStreams "$1" "$2"
;;
testAutolog) testAutolog "$1" "$2" "$3"
;;
*) usage
;;
esac |
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# function that displays its 1st argument on standard output and # its 2nd argument on standard error function stdStreams() { local outTxt=${1:-"text for standard output"} local errTxt=${2:-"text for standard error"} echo "to standard output: '$outTxt'" echo_se "to standard error: '$errTxt'" } |
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argument defaulting
Often you will want to provide a default for arguments not explicitly provided by the user. This can be done using this rather odd syntax, with ":-" characters separating the positional argument number from the desired default. The entire defaulting construct is enclosed in "${ }".
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simpler usage function
We've also added command-line processing and usage support for the new functions.
In the usage function, we've replaced the multiple echo lines in usage with a single echo'd string, illustrating that the invisible line feeds in the echo'd text are faithfully preserved. The function also exits with a non-0 ("failure") return code, since no valid command processing was performed.
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