How do I redirect errors to /dev/null in bash?

Question

We run daily Selenium tests to test our website and extensions. I wrote a script (according to this question) to count the number of passed and failed tests. Here is the script:

#!/bin/bash

today=`TZ='Asia/Tel_Aviv' date +"%Y-%m-%d"`
yesterday=`TZ='Asia/Tel_Aviv' date +"%Y-%m-%d" -d "yesterday"`

...

print_test_results()
{
    declare -i passed_tests=0
    declare -i failed_tests=0
    declare -i total_tests=0
    log_suffix="_${file_name}.log"
    yesterday_logs="${log_prefix}${yesterday}_[1,2]*${log_suffix}"
    today_logs="${log_prefix}${today}_0*${log_suffix}"
    for temp_file_name in $yesterday_logs $today_logs ; do
        total_tests+=1
        if grep -q FAILED "$temp_file_name" ; then
            failed_tests+=1
        elif grep -q OK "$temp_file_name" ; then
            passed_tests+=1
        else
            failed_tests+=1
        fi
    done
    echo "<tr>"
    echo "<td>$test_name - $today</td>"
    if [ $passed_tests = "0" ]; then
        echo "<td>$passed_tests passed</td>"
        echo "<td><span style=\"color: red;\">$failed_tests failed</span></td>"
    else
        echo "<td><span style=\"color: green;\">$passed_tests passed</span></td>"
        echo "<td>$failed_tests failed</td>"
    fi
    echo "<td>$total_tests tests total</td>"
    echo "</tr>"
}

file_name="chrome_gmail_1_with_extension_test"
test_name="Chrome Gmail 1 With Extension Test"
print_test_results

...

But the problem is, if the files are not there (in $yesterday_logs $today_logs), I get error messages. How do I redirect these error messages to /dev/null? I want to redirect them to /dev/null from the script, and not from the line calling the script - I want this script to never show error messages about files which don't exist.

Answer 1

Just for the record:

In general, to suppress error messages in bash, use command 2>/dev/null. So in your case you should use grep -q OK 2>/dev/null.

But as your case also shows (from what I read in the comments) this is a risky thing to do, as it cloaks errors you might have in your code. "I want this script to never print error messages" should only be said when one knows all possible error cases which could possibly occur.

Answer 2

Inside your script you can place this line at start:

shopt -s nullglob

This will not match anything if your glob pattern doesn't find any matching file. Otherwise whole glob pattern is returned when you use something like:

for temp_file_name in $yesterday_logs $today_logs; do ... done