Read characters from a text file using bash

Question

Does anyone know how I can read the first two characters from a file, using a bash script. The file in question is actually an I/O driver, it has no new line characters in it, and is in effect infinitely long.

Answer 1

G'day,

Why not use od to get the slice that you need?

od --read-bytes=2 my_driver

Edit: You can't use head for this as the head command prints to stdout. If the first two chars are not printable, you don't see anything.

The od command has several options to format the bytes as you want.

HTH

cheers,

Answer 2

The read builtin supports the -n parameter:

     vinko@mithril:~$ echo "Two chars" | while read -n 2 i; do echo $i; done
     Tw
     o
     ch
     ar
     s


     vinko@mithril:~$ cat /proc/your_driver | (read -n 2 i; echo $i;)

Answer 3

I think dd if=your_file ibs=2 count=1 will do the trick

Looking at it with strace shows it is effectively doing a two bytes read from the file. Here is an example reading from /dev/zero, and piped into hd to display the zero :

dd if=/dev/zero bs=2 count=1 | hd
1+0 enregistrements lus
1+0 enregistrements écrits
2 octets (2 B) copiés, 2,8497e-05 s, 70,2 kB/s
00000000  00 00                                             |..|
00000002

Answer 4

echo "Two chars" | sed 's/../&\n/g'