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Top Forums Shell Programming and Scripting Is Rule 7 of POSIX shell grammar rules written correctly? Post 302978855 by Don Cragun on Thursday 4th of August 2016 08:37:41 PM
Old 08-04-2016
In addition to what bakunin has already said, rule 7 applies in cases like:
  1. IFS=, for i in abc,def,chi,jul;do echo "$i";done which generates a syntax error because for is not recognized as a keyword because it is not the 1st word in the command,
  2. IFS=, PS2='Enter continuation line: ' read var1 var2 var3 forces the read command to be invoked with values for the environment variables IFS and PS2 that apply only during the execution of the read command (without changing the values of those variables in the current shell execution environment), and
  3. =abc read something tries to run a command named =abc with the operands read and something rather than attempting to set the variable with no name to the string abc in the environment of the command read invoked with the operand something.
 

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read(1) 						      General Commands Manual							   read(1)

NAME
read - read a line from standard input SYNOPSIS
var ... DESCRIPTION
reads a single line from standard input. The line is split into fields as when processed by the shell (refer to shells in the first field is assigned to the first variable var, the second field to the second variable var, and so forth. If there are more fields than there are specified var operands, the remaining fields and their intervening separators are assigned to the last var. If there are more vars than fields, the remaining vars are set to empty strings. The setting of variables specified by the var operands affect the current shell execution environment. Standard input to can be redirected from a text file. Since affects the current shell execution environment, it is usually provided as a normal shell special (built-in) command. Thus, if it is called in a subshell or separate utility execution environment similar to the following, it does not affect the shell variables in the caller's environment: Options recognizes the following options: Do not treat a backslash character in any special way. Consider each backslash to be part of the input line. Opperands recognizes the following operands: var The name of an existing or nonexisting shell variable. EXTERNAL INFLUENCES
Environment Variables determines the internal field separators used to delimit fields. RETURN VALUE
exits with one of the following values: 0 Successful completion. >0 End-of-file was detected or an error occurred. EXAMPLES
Print a file with the first field of each line moved to the end of the line. while read -r xx yy do printf "%s %s " "$yy" "$xx" done < input_file SEE ALSO
csh(1), ksh(1), sh(1), sh-posix(1). STANDARDS CONFORMANCE
read(1)
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