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Standard streams

As described Intro Unix: Standard streams and redirection each with a well-defined stream number:

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~/workshop/step_01.sh helloWorld My name is Anna | tee step_01.log

See Standard streams and piping in the Intro Unix wiki.

When standard output and standard error streams are used

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Importantly, auto_log reports an error and terminates script execution if no tag string is specified, via exit 255 (we'll see much more on error handling shortly).

The conditional test is made using a bash if/else/fi block, where double brackets ('"[[ ]]") enclose the test, always followed by a semicolon (";") or a new line. Note that there must always be a space after the open brackets, and one before the close brackets. Here the test is for string equality (see https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html for a complete list of bash comparison operators).

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• Starts automatic logging to a log file named using its 1st logFileTag argument, by calling the auto_log function.
• Uses echo -e where the -e argument to echo enables interpretation of backslash escapes.
  • e.g. "\t" as a tab Tab character and "\n" will be interpreted as a newline.
• Calls stdStreams with its 2nd and 3rd arguments.
• Calls echo capturing its output in a local variable using backtick execution syntax, then displays the captured text.
  • see Quoting in the shell Intro Unix:Backtick evaluation quoting
• Calls the echo_se function with some text.
• Calls the echo_se function again, capturing its output in a local variable, then displays the captured text.
  
  

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1) Call stdStreams with output and error text:
to standard output: 'text for standard output'
to standard error:  'text for standard error'

2) Capture echo output in a variable and display it:
   echo output was:
text for standard output

3) Call echo_se with error text:
text for standard error

4)Capture echo_se function output in a variable and display it:
text for standard error
echo_se output was: ''

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