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Look at this very basic Bash script:
#!/bin/bash
while read l
do
echo $l
echo "next one"
done <<< $(ps aux)
I have several processes on my computer, and the ps aux command works fine in the terminal.
I only get one iteration in the loop and ps command output is given on the same line. Why doesn't it work as intended?
In bash versions < 4.4-beta you need to add double quotes:
#!/bin/bash
while read l
do
echo $l
echo "next one"
done <<< "$(ps aux)"
See:
Bash no longer splits the expansion of here-strings, as the documentation has always said.
In general, I think it is better to use process substitution:
#!/bin/bash
while read l
do
echo $l
echo "next one"
done < <(ps aux)
(To avoid issues, you might want to use IFS=).
or even better, use a program specialized for reading files or input line by line like e.g. awk.
ps aux | awk '{print $0; print "next one"}'
<<< $(...) should be identical to <<< "$(...)" (specifically when used with <<<, not $(...) in general). I can reproduce your problem with bash-3.2, but not with newer versions.
[n]<<<word ... Pathname expansion and word splitting are not performed."
bashv4.4) returns the same multi-line results from both the command line and as a script. Note: it'd be simpler to changewhile ... done <<< $(ps aux)tops aux | while ... done.set -ooutputs. On my systemprintf '%x\n' $((2#$(set -o | rev | cut -c 1 | tr 'fn' '01' | tr -d '\n')))outputs the hex summary of 31d4000. (That is it takes a list of "on/off" values, converts 'em to binary, then to a single hex value.)