Calculate date difference between Last modified date of a file and NOW using shell script

Question

I am trying to calculate the time elapsed since the log file was last updated.

I guess following commands will be used

lastUpdate=$(date -r myLogFile.log)
now=$(date)

How can I subtract them and get result for number of seconds elapsed?

Use +%s (seconds from EPOC) of date output formatting option. — Costas
– Costas, Commented Mar 3, 2015 at 18:55
you meant lastUpdate=$(date -r myLogFile.log +%s)??? i m not able to get the difference stored in variable and i am new to Shell scripting... — Tarik Setia
– Tarik Setia, Commented Mar 3, 2015 at 19:32

WarzauWynn · Accepted Answer · 2015-03-03 19:45:10Z

5

lastUpdate="$(stat -c %Y myLogFile.log)"
now="$(date +%s)"
let diff="${now}-${lastUpdate}"

answered Mar 3, 2015 at 19:45

WarzauWynn

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VaTo · Accepted Answer · 2015-03-03 19:34:14Z

3

compare the two outputs to get the number of seconds between now and the modified date

stat -c %Y file  vs date +%s

answered Mar 3, 2015 at 19:34

VaTo

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Gilles 'SO- stop being evil' · Accepted Answer · 2015-03-04 00:17:21Z

2

You're almost there! Just tell date to use a format on which computation is easy.

lastUpdate=$(date -r myLogFile.log +%s)
now=$(date +%s)
file_age=$((now - lastUpdate))

answered Mar 4, 2015 at 0:17

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Joseph Persie III · Accepted Answer · 2016-02-04 23:05:16Z

2

One liner:

stat -c %Y /path/to/file | echo `expr $(date +%s) - $(cat)`

answered Feb 4, 2016 at 23:05

Joseph Persie III

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4 Answers 4