Define variable using read from stdin of heredoc
I am trying to store Available and Total Memory into variables in a script file as follows,
read -r Available Total <<EOT
$(free -m | awk '/^Mem/{print $7; print $2;}')
EOT
$ echo $Total
$ echo $Available
1437
But I am unable to store the variable $Total.
But when I do:
$ read Available Total <<EOT
$(echo $(free -m | awk '/^Mem/{print $7; print $2;}'))
EOT
$ echo $Available
1309
$ echo $Total
7865
It works. But shellcheck gives me following suggestion:
Useless echo? Instead of 'echo $(cmd)', just use 'cmd'. [SC2005]
Why the forst example didn't work? and Why the second one works?
bash variable echo here-document shellcheck
asked 2 days ago
NikhilNikhil
256110
add a comment |
I am trying to store Available and Total Memory into variables in a script file as follows,
read -r Available Total <<EOT
$(free -m | awk '/^Mem/{print $7; print $2;}')
EOT
$ echo $Total
$ echo $Available
1437
But I am unable to store the variable $Total.
But when I do:
$ read Available Total <<EOT
$(echo $(free -m | awk '/^Mem/{print $7; print $2;}'))
EOT
$ echo $Available
1309
$ echo $Total
7865
It works. But shellcheck gives me following suggestion:
Useless echo? Instead of 'echo $(cmd)', just use 'cmd'. [SC2005]
Why the forst example didn't work? and Why the second one works?
bash variable echo here-document shellcheck
asked 2 days ago
NikhilNikhil
256110
add a comment |
I am trying to store Available and Total Memory into variables in a script file as follows,
read -r Available Total <<EOT
$(free -m | awk '/^Mem/{print $7; print $2;}')
EOT
$ echo $Total
$ echo $Available
1437
But I am unable to store the variable $Total.
But when I do:
$ read Available Total <<EOT
$(echo $(free -m | awk '/^Mem/{print $7; print $2;}'))
EOT
$ echo $Available
1309
$ echo $Total
7865
It works. But shellcheck gives me following suggestion:
Useless echo? Instead of 'echo $(cmd)', just use 'cmd'. [SC2005]
Why the forst example didn't work? and Why the second one works?
bash variable echo here-document shellcheck
asked 2 days ago
NikhilNikhil
256110
I am trying to store Available and Total Memory into variables in a script file as follows,
read -r Available Total <<EOT
$(free -m | awk '/^Mem/{print $7; print $2;}')
EOT
$ echo $Total
$ echo $Available
1437
But I am unable to store the variable $Total.
But when I do:
$ read Available Total <<EOT
$(echo $(free -m | awk '/^Mem/{print $7; print $2;}'))
EOT
$ echo $Available
1309
$ echo $Total
7865
It works. But shellcheck gives me following suggestion:
Useless echo? Instead of 'echo $(cmd)', just use 'cmd'. [SC2005]
Why the forst example didn't work? and Why the second one works?
bash variable echo here-document shellcheck
bash variable echo here-document shellcheck
asked 2 days ago
NikhilNikhil
256110
asked 2 days ago
NikhilNikhil
256110
asked 2 days ago
NikhilNikhil
256110
asked 2 days ago
NikhilNikhil
256110
asked 2 days ago
NikhilNikhil
256110
256110
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
That awk command prints the two values on two separate lines, while read reads one line, expecting to find two fields on it.
Change the print command to print $7, $2; to print the numbers on the same line. Since you tagged this with Bash, you can use a here-string instead of a here-doc to make the full command a bit neater:
$ read -r Available Total <<< $( free -m | awk '/^Mem/{print $7, $2;}' )
Or use a process substitution:
$ read -r Available Total < <( free -m | awk '/^Mem/{print $7, $2;}' )
If you use echo $(...) without quotes around the command substitution, the output from the command gets word-split, and echo sees the separate lines as separate arguments. It prints all of its arguments joined with spaces, so on a single line.
echo $(foo) is usually rather a useless thing to do, but isn't the same same just foo, for this very reason. It also puts a final newline at the end of the output of foo, if it wasn't there already.
answered 2 days ago
ilkkachuilkkachu
56.6k784156
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't workread -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}')Could you please correct this?
– Nikhil
2 days ago
2
@Nikhil, process substitution needs the redirection operator<here. In itself it just expands to a (pseudo)filename, whichreadwould take as the name of a variable to write to. (It's probably something like/dev/fd/63, which isn't a valid variable name so you get an error.)
– ilkkachu
2 days ago
1
Yes,readreads stdin, so you need a redirection.
– glenn jackman
2 days ago
add a comment |
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That awk command prints the two values on two separate lines, while read reads one line, expecting to find two fields on it.
Change the print command to print $7, $2; to print the numbers on the same line. Since you tagged this with Bash, you can use a here-string instead of a here-doc to make the full command a bit neater:
$ read -r Available Total <<< $( free -m | awk '/^Mem/{print $7, $2;}' )
Or use a process substitution:
$ read -r Available Total < <( free -m | awk '/^Mem/{print $7, $2;}' )
If you use echo $(...) without quotes around the command substitution, the output from the command gets word-split, and echo sees the separate lines as separate arguments. It prints all of its arguments joined with spaces, so on a single line.
echo $(foo) is usually rather a useless thing to do, but isn't the same same just foo, for this very reason. It also puts a final newline at the end of the output of foo, if it wasn't there already.
answered 2 days ago
ilkkachuilkkachu
56.6k784156
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't workread -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}')Could you please correct this?
– Nikhil
2 days ago
2
@Nikhil, process substitution needs the redirection operator<here. In itself it just expands to a (pseudo)filename, whichreadwould take as the name of a variable to write to. (It's probably something like/dev/fd/63, which isn't a valid variable name so you get an error.)
– ilkkachu
2 days ago
1
Yes,readreads stdin, so you need a redirection.
– glenn jackman
2 days ago
add a comment |
That awk command prints the two values on two separate lines, while read reads one line, expecting to find two fields on it.
Change the print command to print $7, $2; to print the numbers on the same line. Since you tagged this with Bash, you can use a here-string instead of a here-doc to make the full command a bit neater:
$ read -r Available Total <<< $( free -m | awk '/^Mem/{print $7, $2;}' )
Or use a process substitution:
$ read -r Available Total < <( free -m | awk '/^Mem/{print $7, $2;}' )
If you use echo $(...) without quotes around the command substitution, the output from the command gets word-split, and echo sees the separate lines as separate arguments. It prints all of its arguments joined with spaces, so on a single line.
echo $(foo) is usually rather a useless thing to do, but isn't the same same just foo, for this very reason. It also puts a final newline at the end of the output of foo, if it wasn't there already.
answered 2 days ago
ilkkachuilkkachu
56.6k784156
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't workread -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}')Could you please correct this?
– Nikhil
2 days ago
2
@Nikhil, process substitution needs the redirection operator<here. In itself it just expands to a (pseudo)filename, whichreadwould take as the name of a variable to write to. (It's probably something like/dev/fd/63, which isn't a valid variable name so you get an error.)
– ilkkachu
2 days ago
1
Yes,readreads stdin, so you need a redirection.
– glenn jackman
2 days ago
add a comment |
That awk command prints the two values on two separate lines, while read reads one line, expecting to find two fields on it.
Change the print command to print $7, $2; to print the numbers on the same line. Since you tagged this with Bash, you can use a here-string instead of a here-doc to make the full command a bit neater:
$ read -r Available Total <<< $( free -m | awk '/^Mem/{print $7, $2;}' )
Or use a process substitution:
$ read -r Available Total < <( free -m | awk '/^Mem/{print $7, $2;}' )
If you use echo $(...) without quotes around the command substitution, the output from the command gets word-split, and echo sees the separate lines as separate arguments. It prints all of its arguments joined with spaces, so on a single line.
echo $(foo) is usually rather a useless thing to do, but isn't the same same just foo, for this very reason. It also puts a final newline at the end of the output of foo, if it wasn't there already.
answered 2 days ago
ilkkachuilkkachu
56.6k784156
That awk command prints the two values on two separate lines, while read reads one line, expecting to find two fields on it.
Change the print command to print $7, $2; to print the numbers on the same line. Since you tagged this with Bash, you can use a here-string instead of a here-doc to make the full command a bit neater:
$ read -r Available Total <<< $( free -m | awk '/^Mem/{print $7, $2;}' )
Or use a process substitution:
$ read -r Available Total < <( free -m | awk '/^Mem/{print $7, $2;}' )
If you use echo $(...) without quotes around the command substitution, the output from the command gets word-split, and echo sees the separate lines as separate arguments. It prints all of its arguments joined with spaces, so on a single line.
echo $(foo) is usually rather a useless thing to do, but isn't the same same just foo, for this very reason. It also puts a final newline at the end of the output of foo, if it wasn't there already.
answered 2 days ago
ilkkachuilkkachu
56.6k784156
edited 2 days ago
answered 2 days ago
ilkkachuilkkachu
56.6k784156
answered 2 days ago
ilkkachuilkkachu
56.6k784156
answered 2 days ago
ilkkachuilkkachu
56.6k784156
56.6k784156
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't workread -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}')Could you please correct this?
– Nikhil
2 days ago
2
@Nikhil, process substitution needs the redirection operator<here. In itself it just expands to a (pseudo)filename, whichreadwould take as the name of a variable to write to. (It's probably something like/dev/fd/63, which isn't a valid variable name so you get an error.)
– ilkkachu
2 days ago
1
Yes,readreads stdin, so you need a redirection.
– glenn jackman
2 days ago
add a comment |
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't workread -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}')Could you please correct this?
– Nikhil
2 days ago
2
@Nikhil, process substitution needs the redirection operator<here. In itself it just expands to a (pseudo)filename, whichreadwould take as the name of a variable to write to. (It's probably something like/dev/fd/63, which isn't a valid variable name so you get an error.)
– ilkkachu
2 days ago
1
Yes,readreads stdin, so you need a redirection.
– glenn jackman
2 days ago
1
1
Process Substitution would work here as well.
– glenn jackman
2 days ago
Process Substitution would work here as well.
– glenn jackman
2 days ago
@glennjackman This doesn't work
read -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}') Could you please correct this?– Nikhil
2 days ago
@glennjackman This doesn't work
read -r Available Total <(free -m | awk '/^Mem/{print $7, $2;}') Could you please correct this?– Nikhil
2 days ago
2
2
@Nikhil, process substitution needs the redirection operator
< here. In itself it just expands to a (pseudo)filename, which read would take as the name of a variable to write to. (It's probably something like /dev/fd/63, which isn't a valid variable name so you get an error.)– ilkkachu
2 days ago
@Nikhil, process substitution needs the redirection operator
< here. In itself it just expands to a (pseudo)filename, which read would take as the name of a variable to write to. (It's probably something like /dev/fd/63, which isn't a valid variable name so you get an error.)– ilkkachu
2 days ago
1
1
Yes,
read reads stdin, so you need a redirection.– glenn jackman
2 days ago
Yes,
read reads stdin, so you need a redirection.– glenn jackman
2 days ago
add a comment |
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