difftime is a simple utility to calculate and print out the delta time from two files or a file and now. It's usefull to make a gate in a script, based on time.

Just compile and install

make
sudo make install

With no arguments, it fail with exit code not zero.

The first argument must be a file. With no second argument, it print out the time differnce between the last modification time of the file and now. If the file doesn't exists it fail with exit code not zero. The output is in seconds by default.

difftime -P -A /var/spool/gate
2345

Passing the second argument, the difference is between the modification time of the second and the first.

difftime -P /var/spool/older /var/spool/newer
1234
difftime -P /var/spool/newer /var/spool/older
-1234

You can customize the output and choose which time to compare. The output options are in upper case, the time options lower.

The default output is in seconds. Other options are:

• -M in minutes
• -H in hours
• -D in days

It returns 0 if the amount of seconds cannot reach a single unit of the selected time.

By default difftime print out the number without the \n character at the end, so you can use it in a variable:

DT=$(difftime -A /var/spool/gate) 
[ $DT -gt 120 ] && echo "too old"

If you need to get the result to print out, use the -P option, that add the newline character at the end.

difftime -P -A /var/spool/gate
12345

By default the output is signed (- as prefix if negative). If you want an absolute value, use the -A option.

difftime -P -A /var/spool/older /var/spool/newer
1234

By default difftime compare the modification date of the files. You can change that with the time options:

• -a access time
• -m modification time
• -c change time

Each option is valid for the corresponding file. For example you can check the access time of the first file and the change time of the second.

difftime -P -D -A -a /var/spool/base -c /var/spool/gate
3

By default all the timestamp is compared. To diff only a part (field) of the timestamp, such as the day, use the option -f or --field with argument:

• Y year
• M month
• D day
• h hour
• m minute
• s second

The output options are ignored because the unit of the output number is the same of the field.

To check how many days before was modified a file, no matters the exact time

difftime -P -A -f D file
1

1 stands for one day of difference, so it was modified yesterday.

You can access to the help and show the version with these options:

• -h for the help
• -v for the version

Displaying the times of the file is not the purpose of difftime. You can check them with the standard UNIX command stat.

#!/bin/bash

# Very simple time gate

SPOOL_FILE="spool"
# time in seconds
TIME_GATE=10

DT=$(./difftime -A $SPOOL_FILE 2> /dev/null ) || DT=$TIME_GATE

[ $DT -lt $TIME_GATE ] && exit 1

echo "Do the stuff"

# reset the spool time
touch $SPOOL_FILE