postIt » shell script

grep omit empty lines: cat | grep -v …

Arif — Wed, 25 Jan 2012 06:44:07 +0000

grep omit empty lines:

cat <something> | grep -v "^$"

I keep forgetting this regexp of “match expression at the star of the line”: the “^”

Checking whether /dev/video0 or /dev/tty …

Arif — Tue, 10 Jan 2012 06:39:59 +0000

Checking whether /dev/video0 or /dev/ttyUSB0 exists or not (module is installed & probed). They're recognized as "character special file" in bash



[ -b /dev/ttyUSB0 ] && echo "char special file found" || echo "char special file not found"

Compare the above to "block special file"

[ -b /dev/sda ] && echo "block special file found" || echo "block special file not found"



Unix time conversion   # EPOCH=129751 …
Arif — Sat, 12 Feb 2011 13:52:10 +0000
Unix time conversion

$ EPOCH=1297515579843
$ echo $EPOCH | cut -c1-10
1297515579
 
$ echo $EPOCH | cut -c1-10 | awk '{print strftime("%c",$1)}'
Sat 12 Feb 2011 07:59:39 PM WIT




$ sleep 120 && touch 120 & sleep 4 && to …
Arif — Wed, 17 Mar 2010 10:34:14 +0000
$ sleep 120 && touch 120 & sleep 4 && touch 4
So, how are those file touch comes up in sequence (watch the creation time)

$ ls -l
total 160
-rw-r--r-- 1 arif arif     0 2010-03-17 17:28 120
-rw-r--r-- 1 arif arif     0 2010-03-17 17:27 4
...