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Full Discussion: How to understand special character for line reading in bash shell?
Top Forums Shell Programming and Scripting How to understand special character for line reading in bash shell? Post 303039060 by duke0001 on Saturday 21st of September 2019 01:22:04 PM
Old 09-21-2019
How to understand special character for line reading in bash shell?
I am still learning shell scripting. Recently I see a function for read configuration. But some of special character make me confused. I checked online to find answer. It was not successful. I post the code here to consult with expert or guru to get better understanding on these special characters such as:^[^#]*=, line%%=*, line#*=. how to understand the usage of these special character here. Thanks.

Code:
read_cfg()
{”‹
  while read line; do”‹
     if [[ "$line" =~ ^[^#]*= ]]; then”‹
        l_parameter=`echo ${line%%=*} | tr -d ' '` l_value=`echo ${line#*=} | tr -d ' '`”‹
”‹
        case "$l_parameter" in ”‹
           "EMAIL_LIST" ) ”‹      #email list provided in command line overwrites the one in configuration file”‹
               if [ -z "$g_bkp_email" ] ; then”‹
                  g_bkp_email=$l_value”‹
               fi”‹
               ;;”‹

 

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LEARN ABOUT DEBIAN

shtool-echo

SHTOOL-ECHO.TMP(1)					      GNU Portable Shell Tool						SHTOOL-ECHO.TMP(1)

NAME

       shtool-echo - GNU shtool echo(1) extensional command

SYNOPSIS

       shtool echo [-n|--newline] [-e|--expand] string

DESCRIPTION

       shtool echo is an echo(1) style command which prints string to stdout and optionally provides special expansion constructs (terminal bold
       mode, environment details, date, etc) and newline control. The trick of this command is that it provides a portable -n option and hides the
       gory details needed to find out the environment details under option -e.

OPTIONS

       The following command line options are available.

       -n, --newline
	   By default, output is written to stdout followed by a "newline" (ASCII character 0x0a). If option -n is used, this newline character is
	   omitted.

       -e, --expand
	   If option -e is used, string can contain special "%x" constructs which are expanded before the output is written. Currently the
	   following constructs are recognized:

	   %B  switch terminal mode to bold display mode.

	   %b  switch terminal mode back to normal display mode.

	   %u  the current user name.

	   %U  the current user id (numerical).

	   %g  the current group name.

	   %G  the current group id (numerical).

	   %h  the current hostname (without any domain extension).

	   %d  the current domain name.

	   %D  the current day of the month.

	   %M  the current month (numerical).

	   %m  the current month name.

	   %Y  the current year.

EXAMPLE

	#   shell script
	shtool echo -n -e "Enter your name [%B%u%b]: "; read name
	shtool echo -e "Your Email address might be %u@%h%d"
	shtool echo -e "The current date is %D-%m-%Y"

HISTORY

       The GNU shtool echo command was originally written by Ralf S.  Engelschall <rse@engelschall.com> in 1998 for Website META Language (WML)
       under the name buildinfo. It was later taken over into GNU shtool.

SEE ALSO

       shtool(1), echo(1).

18-Jul-2008							   shtool 2.0.8 						SHTOOL-ECHO.TMP(1)
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