Help on for loop in bash Post: 302976095

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Top Forums Shell Programming and Scripting Help on for loop in bash Post 302976095 by Don Cragun on Thursday 23rd of June 2016 10:13:57 PM

06-23-2016

Registered User

We may have a language barrier here. I am asking questions in shell, your answering in English.

If you have a bunch of files with names ending with the four characters .txt, I can use the shell filename matching pattern *.txt to get a list (produced by the shell before it invokes your script) of all of the files matching that filename matching pattern. The data passed as command-line arguments to your script will be filenames, not patterns. But, if the command-line argument was quoted ("*.txt"), then the arguments that your script would get would be filename matching patterns; not filenames. You have said that you aren't quoting your arguments, so using a variable named pattern to hold these filenames (not patterns) is misleading and confusing to people trying to understand your script.

But, when you're reading from standard input, if you're just typing text that will be read by your script, the shell will not perform filename matching pattern expansions to filenames of any patterns you type into your script; so if you are expecting the shell to expand filename matching patterns on command-line operands, you must just type in filenames; not filename matching patterns for lines that type into your script that you want it to read from standard input.

The following script shows you how you can read command-line operands or (if no operands are present after option parsing has been completed) or lines from standard input:

Code:

#!/bin/sh
if [ $# -gt 0 ]
then	for arg in "$@"
	do	printf '%s\n' "$arg"
	done
else	while IFS= read -r line
	do	printf '%s\n' "$line"
	done
fi | while IFS= read -r file
do	printf 'operand or stdin line #%d: "%s"\n' $((++cnt)) "$file"
done

This will work with any shell that uses basic POSIX shell requirements. It won't work with a traditional Bourne shell (since it doesn't support $((expression)) arithmetic substitutions).

Don Cragun

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LEARN ABOUT DEBIAN

confget

CONFGET(1)						    BSD General Commands Manual 						CONFGET(1)

NAME

     confget -- read a variable from a configuration file

SYNOPSIS

     confget [-cSx] [-N | -n] [-f filename] [-m pattern] [-P postfix] [-p prefix] [-s section] [-t type] varname...
     confget [-] [-N | -n] [-f filename] [-m pattern] [-P postfix] [-p prefix] [-s section] [-t type] -L pattern...
     confget [-] [-N | -n] [-f filename] [-m pattern] [-P postfix] [-p prefix] [-s section] [-t type] -l
     confget [-hTV]

DESCRIPTION

     The confget utility examines a INI-style configuration file and retrieves the value of the specified variables from the specified section.
     Its intended use is to let shell scripts use the same INI-style configuration files as other programs, to avoid duplication of data.

     The confget utility may retrieve the values of one or more variables, list all the variables in a specified section, list only those whose
     names or values match a specified pattern (shell glob or regular expression), or check if a variable is present in the file at all.  It has a
     ``shell-quoting'' output mode that quotes the variable values in a way suitable for passing them directly to a Bourne-style shell.

     Options:

     -c      Check-only mode; exit with a code of 0 if any of the variables are present in the configuration file, and 1 if there are none.

     -f filename
	     Specify the configuration file to read from, or ``-'' (a single dash) for standard input.

     -h      Display program usage information and exit.

     -L      Variable list mode; display the names and values of all variables in the specified section with names matching one or more specified
	     patterns.

     -l      List mode; display the names and values of all variables in the specified section.

     -m pattern
	     Only display variables with if their values match the specified pattern.

     -N      Always display the variable name along with the value.

     -n      Never display the variable name, only the value.

     -P postfix
	     Display this string after the variable name as a postfix.

     -p prefix
	     Display this string before the variable name as a prefix.

     -S      Quote the variable values so that the ``var=value'' lines may be passed directly to the Bourne shell.

     -s section
	     Specify the configuration section to read.

	     If this option is not specified, confget will use the first section found in the configuration file.  However, if the configuration
	     file contains variable definitions before a section header, confget will only examine them instead.

     -T      List the available configuration file types that may be selected by the -t option.

     -t type
	     Specify the configuration file type.

     -V      Display program version information and exit.

     -x      Treat the patterns as regular expressions instead of shell glob patterns.

ENVIRONMENT

     Not taken into consideration.

EXIT STATUS

     If the -c option is specified, the confget utility will exit with a status of 0 if any of the specified variables exist in the config file
     and 1 if none of them are present.

     In normal operation, no matter whether any variables were found in the configuration file or not, the confget utility exits with a status of
     0 upon normal completion.	If any errors should occur while accessing or parsing the configuration file, the confget utility will display a
     diagnostic message on the standard error stream and exit with a status of 1.

EXAMPLES

     Retrieve the variable machine_id from the system section of a configuration file:

	   confget -f h.conf -s system machine_id

     Retrieve the page_id variable from an HTTP GET request, but only if it is a valid number:

	   confget -f- -t http_get -x -m '^+$' page_id

     Retrieve the variable hostname from the db section, but only if it ends in ``.ringlet.net'':

	   confget -f h.conf -s db -m '*.ringlet.net' hostname

     Display the names and values of all variables in the system section with names beginning with ``mach'' or ending in ``name'', appending a
     ``cfg_'' at the start of each variable name:

	   confget -f h.conf -s system -p 'cfg_' -L 'mach*' '*name'

     Display the names and values of all variables in the system section:

	   confget -f h.conf -s system -l

     Safely read the contents of the db section:

	   eval `confget -f h.conf -s db -p db_ -S -l`

SEE ALSO

     For another way to parse INI files, see the Config::IniFiles(3) Perl module.

STANDARDS

     No standards documentation was harmed in the process of creating confget.

BUGS

     Please report any bugs in confget to the author.

AUTHOR

     The confget utility was conceived and written by Peter Pentchev <roam@ringlet.net> in 2008.

BSD
								 October 25, 2008							       BSD

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