Linux command (like cat) to read a specified quant

Question

Is there a command like cat in linux which can return a specified quantity of characters from a file?

e.g., I have a text file like:

Hello world
this is the second line
this is the third line

And I want something that would return the first 5 characters, which would be "hello".

thanks

Answer 1

I know the answer is in reply to a question asked 6 years ago ...

But I was looking for something similar for a few hours and then found out that: cut -c does exactly that, with an added bonus that you could also specify an offset.

cut -c 1-5 will return Hello and cut -c 7-11 will return world. No need for any other command

Answer 2

Here's a simple script that wraps up using the dd approach mentioned here:

extract_chars.sh

#!/usr/bin/env bash

function show_help()
{
  IT="
extracts characters X to Y from stdin or FILE
usage: X Y {FILE}

e.g. 

2 10 /tmp/it     => extract chars 2-10 from /tmp/it
EOF
  "
  echo "$IT"
  exit
}

if [ "$1" == "help" ]
then
  show_help
fi
if [ -z "$1" ]
then
  show_help
fi

FROM=$1
TO=$2
COUNT=`expr $TO - $FROM + 1`

if [ -z "$3" ]
then
  dd skip=$FROM count=$COUNT bs=1 2>/dev/null
else
  dd skip=$FROM count=$COUNT bs=1 if=$3 2>/dev/null 
fi

Answer 3

head -Line_number file_name | tail -1 |cut -c Num_of_chars

this script gives the exact number of characters from the specific line and location, e.g.:

head -5 tst.txt | tail -1 |cut -c 5-8

gives the chars in line 5 and chars 5 to 8 of line 5,

Note: tail -1 is used to select the last line displayed by the head.

Answer 4

head or tail can do it as well:

head -c X

Prints the first X bytes (not necessarily characters if it's a UTF-16 file) of the file. tail will do the same, except for the last X bytes.

This (and cut) are portable.

Answer 5

Even though this was answered/accepted years ago, the presently accepted answer is only correct for one-byte-per-character encodings like iso-8859-1, or for the single-byte subsets of variable-byte character sets (like Latin characters within UTF-8). Even using multiple-byte splices instead would still only work for fixed-multibyte encodings like UTF-16. Given that now UTF-8 is well on its way to being a universal standard, and when looking at this list of languages by number of native speakers and this list of top 30 languages by native/secondary usage, it is important to point out a simple variable-byte character-friendly (not byte-based) technique, using cut -c and tr/sed with character-classes.

Compare the following which doubly fails due to two common Latin-centric mistakes/presumptions regarding the bytes vs. characters issue (one is head vs. cut, the other is [a-z][A-Z] vs. [:upper:][:lower:]):

$ printf 'Πού μπορώ να μάθω σανσκριτικά;\n' | \
$     head -c 1 | \
$     sed -e 's/[A-Z]/[a-z]/g'
[[unreadable binary mess, or nothing if the terminal filtered it]]

to this (note: this worked fine on FreeBSD, but both cut & tr on GNU/Linux still mangled Greek in UTF-8 for me though):

$ printf 'Πού μπορώ να μάθω σανσκριτικά;\n' | \
$     cut -c 1 | \
$     tr '[:upper:]' '[:lower:]'
π

Another more recent answer had already proposed "cut", but only because of the side issue that it can be used to specify arbitrary offsets, not because of the directly relevant character vs. bytes issue.

If your cut doesn't handle -c with variable-byte encodings correctly, for "the first X characters" (replace X with your number) you could try:

• sed -E -e '1 s/^(.{X}).*$/\1/' -e q - which is limited to the first line though
• head -n 1 | grep -E -o '^.{X}' - which is limited to the first line and chains two commands though
• dd - which has already been suggested in other answers, but is really cumbersome
• A complicated sed script with sliding window buffer to handle characters spread over multiple lines, but that is probably more cumbersome/fragile than just using something like dd

If your tr doesn't handle character-classes with variable-byte encodings correctly you could try:

• sed -E -e 's/[[:upper:]]/\L&/g (GNU-specific)

Answer 6

head works too:

head -c 100 file  # returns the first 100 bytes in the file

..will extract the first 100 bytes and return them.

What's nice about using head for this is that the syntax for tail matches:

tail -c 100 file  # returns the last 100 bytes in the file