I am curious to know that whether it is possible in bash that we can run for loop on a bunch of variables and call those values within for loop. Example:
a="hello"
b="world"
c="this is bash"
for f in a b c; do {
echo $( $f )
OR
echo $ ( "$f" )
} done
I know this is not working but can we call the values saved in a, b and c variables in for loop with printing f. I tried multiple way but unable to resolve.
You need the ! like this:
for f in a b c; do
echo "${!f}"
done
You can also use a nameref:
#!/usr/bin/env bash
a="hello"
b="world"
c="this is bash"
declare -n f
for f in a b c; do
printf "%s\n" "$f"
done
From the documentation:
If the control variable in a for loop has the nameref attribute, the list of words can be a list of shell variables, and a name reference will be established for each word in the list, in turn, when the loop is executed.
Notes on the OP's code, (scroll to bottom for corrected version):
for f in a b c; do {
echo $( $f )
} done
Problems:
The purpose of { & } is usually to put the separate outputs of
separate unpiped commands into one stream. Example of separate
commands:
echo foo; echo bar | tac
Output:
foo
bar
The tac command puts lines of input in reverse order, but in the
code above it only gets one line, so there's nothing to reverse.
But with curly braces:
{ echo foo; echo bar; } | tac
Output:
bar
foo
A do ... done already acts just like curly braces.
So "do {" instead of a "do" is unnecessary and redundant; but it
won't harm anything, or have any effect.
If f=hello and we write:
echo $f
The output will be:
hello
But the code $( $f ) runs a subshell on $f which only works if $f is
a command. So:
echo $( $f )
...tries to run the command hello, but there probably is no such
command, so the subshell will output to standard error:
hello: command not found
...but no data is sent to standard output, so echo will
print nothing.
To fix:
a="hello"
b="world"
c="this is bash"
for f in "$a" "$b" "$c"; do
echo "$f"
done
for f in $a $b $candecho $ffor f in "$a" "$b" "$c"andecho "$f"