CODEWITHSUNDEEP
shelloutputstdoutlogfile
y17chen
y17chen

Reputation: 57

shell how to direct all message to file while keeping a handful to screen

echo start commanda
output=$(commanda soemthing)
echo $output

echo start commandb
output=$(commandb something)
echo $output`

How do i do it in shell such that i keep:

echo start commanda
echo start commandb

in stdout, while keeping:

echo start commanda
echo $output
echo start commandb
echo $output

in a logfile?

Upvotes: 1

Views: 52

Answers (1)

John1024
John1024

Reputation: 113924

When you want stdout to go to a file, use redirection. When you want it to go two places, use tee:

echo start commanda | tee -a logfile
output=$(commanda soemthing)
echo $output >>logfile

echo start commandb | tee -a logfile
output=$(commandb something)
echo $output >>logfile

How it works:

  • >>logfile is called redirection. It captures stdout and appends it to the file logfile.

  • | tee -a logfile captures the stdout of the previous command, appends a copy to logfile and duplicates it again to stdout. If you want the file to be overwritten rather than appended to, then omit the -a.

Alternate method

The following sends all output to logfile. Any output line that starts with start is also sent to stdout:

{
    echo start commanda
    output=$(commanda soemthing)
    echo $output

    echo start commandb
    output=$(commandb something)
    echo $output
} | tee -a logfile | grep '^start'

The braces, {...}, group the statements together so that we only need redirect for the whole group. This reduces the number of times that the file logfile is opened and closed. The disadvantage of this approach is that, if the output starts with start, it will also be sent to stdout.

Upvotes: 1

Related Questions