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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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PASTE(1)						    BSD General Commands Manual 						  PASTE(1)

NAME
paste -- merge corresponding or subsequent lines of files SYNOPSIS
paste [-s] [-d list] file ... DESCRIPTION
The paste utility concatenates the corresponding lines of the given input files, replacing all but the last file's newline characters with a single tab character, and writes the resulting lines to standard output. If end-of-file is reached on an input file while other input files still contain data, the file is treated as if it were an endless source of empty lines. The options are as follows: -d list Use one or more of the provided characters to replace the newline characters instead of the default tab. The characters in list are used circularly, i.e., when list is exhausted the first character from list is reused. This continues until a line from the last input file (in default operation) or the last line in each file (using the -s option) is displayed, at which time paste begins selecting characters from the beginning of list again. The following special characters can also be used in list: newline character tab character \ backslash character Empty string (not a null character). Any other character preceded by a backslash is equivalent to the character itself. -s Concatenate all of the lines of each separate input file in command line order. The newline character of every line except the last line in each input file is replaced with the tab character, unless otherwise specified by the -d option. If '-' is specified for one or more of the input files, the standard input is used; standard input is read one line at a time, circularly, for each instance of '-'. The paste utility exits 0 on success, and >0 if an error occurs. SEE ALSO
cut(1) STANDARDS
The paste utility is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. BSD
June 6, 1993 BSD
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