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Top Forums UNIX for Dummies Questions & Answers Understanding the concept behind subshells Post 302888850 by RudiC on Monday 17th of February 2014 05:51:58 PM
Old 02-17-2014
Posting your /etc/passwd here wouldn't be a good idea.
Using several grep processes to read some fields from it is no good idea either. And assigning fields to enumerated variables can exceed the number of variables if you don't exactly know how many data lines you are going to read. Grepping for 5000 just along the line may not be specific enough; unwanted fields may fulfill this condition and give false hits.
Why don't you try sth like
Code:
while IFS=: read UN X UID GID USER REST; do echo Username: $UN, $UID, $USER; done </etc/passwd

 

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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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