06-13-2002
The shell spawns a subshell to run the command. The subshell creates an environment variable called variable1 and gives it the value qwerty. Then it runs the ls | sort pipeline. If instead of "ls |sort" you had run "env" or "printenv" you would have seen the new variable. But the original shell's environment remains untouched.
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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)