mjhjmtu

If I have really long output from a command (single line) but I know I only want the first [x] (let's say 8) characters of the output, what's the easiest way to get that? There aren't any delimiters.

One way is to use cut:

 command | cut -c1-8

This will give you the first 8 characters of each line of output. Since cut is part of POSIX, it is likely to be on most Unices.

These are some other ways to get only first 8 characters.

command | head -c8

command | awk 'print substr($0,1,8);exit' 

command | sed 's/^(........).*/1/;q'

And if you have bash

var=$(command)
echo $var:0:8

If you have a sufficiently advanced shell (for example, the following will work in Bash, not sure about dash), you can do:

read -n8 -d$'' -r <(command)

After executing read ... <(command), your characters will be in the shell variable REPLY. Type help read to learn about other options.

Explanation: the -n8 argument to read says that we want up to 8 characters. The -d$'' says read until a null, rather than to a newline. This way the read will continue for 8 characters even if one of the earlier characters is a newline (but not if its a null). An alternative to -n8 -d$'' is to use -N8, which reads for exactly 8 characters or until the stdin reaches EOF. No delimiter is honored. That probably fits your needs better, but I don't know offhand how many shells have a read that honors -N as opposed to honoring -n and -d. Continuing with the explanation: -r says ignore -escapes, so that, for example, we treat \ as two characters, rather than as a single .

Finally, we do read ... <(command) rather than command | read ... because in the second form, the read is executed in a subshell which is then immediately exited, losing the information you just read.

Another option is to do all your processing inside the subshell. For example:

$ echo abcdefghijklm | read -n8 -d$'' -r; printf "REPLY=<%s>n" "$REPLY"; 
REPLY=<abcdefgh>

This is portable:

a="$(command)" # Get the output of the command.
b="????" # as many ? as characters are needed.
echo $a%"$a#$b" # select that many chars from $a

To build a string of variable length of characters has its own question here.

I had this problem when manually generating checksum files in maven repository.
Unfortunately cut -c always prints out a newline at the end of output.
To suppress that I use xxd:

command | xxd -l$BYTES | xxd -r

It outputs exactly $BYTES bytes, unless the command's output is shorter, then exactly that output.

Another one liner solution by using parameter expansion

echo $word:0:x

EG: word="Hello world"
echo $word:0:3 or echo $word::3 
o/p: Hel


EG.2: word="Hello world"
echo $word:1:3
o/p: ell