Passing two arguments to a command using pipes
- by firebat
Usually, we only need to pass one argument:
echo abc | cat
echo abc | cat some_file -
echo abc | cat - some_file
Is there a way to pass two arguments? Something like
{echo abc , echo xyz} | cat
cat `echo abc` `echo xyz`
I could just store both results in a file first
echo abc > file1
echo xyz > file2
cat file1 file2
But then I might accidentally overwrite a file, which is not ok. This is going into a non-interactive script. Basically, I need a way to pass the results of two arbitrary commands to cat without writing to a file.
UPDATE:
Sorry, the example masks the problem. While { echo abc ; echo xyz ; } | cat does seem to work, the output is due to the echos, not the cat.
A better example would be { cut -f2 -d, file1; cut -f1 -d, file2; } | paste -d, which does not work as expected.
With
file1:
a,b
c,d
file2:
1,2
3,4
Expected output is:
b,1
d,3
RESOLVED:
Use process substitution: cat <(command1) <(command2)
Alternatively, make named pipes using mkfifo:
mkfifo temp1
mkfifo temp2
command1 > temp1 &
command2 > temp2 &
cat temp1 temp2
Less elegant and more verbose, but works fine, as long as you make sure temp1 and temp2 don't exist before hand.
