Ubuntu – n easy way to log all activity that a shell script does

Use output redirection to /dev/null and include stderr output.

add-apt-repository -y ppa:ondrej/php5-oldstable > /dev/null 2>&1

• The 2>&1 will tell Bash to redirect stderr to stdout.
• The command > file stanza will redirect stdout to a file, in this case /dev/null.
• /dev/null is the black hole of Linux - you won't be able to recovery anything from there.

Result: full silent execution of your command.

In your updated question you seem to log all output to a file. In that case you can just append the 2>&1 to your current line:

add-apt-repository -y ppa:ondrej/php5-oldstable >> /tmp/output.txt 2>&1

This is because you were looking at the stderr output being printed on the terminal, which you need to redirect to the log as well (otherwise you will miss out on all errors!).

To hide the output of any command usually the stdout and stderr are redirected to /dev/null.

command > /dev/null 2>&1

Explanation:

1.command > /dev/null: redirects the output of command(stdout) to /dev/null
2.2>&1: redirects stderr to stdout, so errors (if any) also goes to /dev/null

Note

&>/dev/null: redirects both stdout and stderr to /dev/null. one can use it as an alternate of /dev/null 2>&1

Silent grep: grep -q "string" match the string silently or quietly without anything to standard output. It also can be used to hide the output.

In your case, you can use it like,

if dpkg -s net-tools > /dev/null 2>&1; then
    if  netstat -tlpn | grep 8080 | grep java > /dev/null 2>&1; then
    #rest thing
else
    echo "your message"
fi

Here the if conditions will be checked as it was before but there will not be any output.

Reply to the comment:

netstat -tlpn | grep 8080 | grep java > /dev/null 2>&1: It is redirecting the output raised from grep java after the second pipe. But the message you are getting from netstat -tlpn. The solution is use second if as,

if  [[ `netstat -tlpn | grep 8080 | grep java` ]] &>/dev/null; then