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
This question is related to
linux
command-line
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
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.
you could also grep the line out and then cut it like for instance:
grep 'text' filename | cut -c 1-5
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 '??? µp??? ?a µ??? sa?s???t???;\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 '??? µp??? ?a µ??? sa?s???t???;\n' | \
$ cut -c 1 | \
$ tr '[:upper:]' '[:lower:]'
p
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 thoughhead -n 1 | grep -E -o '^.{X}'
- which is limited to the first line and chains two commands thoughdd
- which has already been suggested in other answers, but is really cumbersomesed
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)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.
head:
head - output the first part of files
head [OPTION]... [FILE]...
Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-c, --bytes=[-]N
print the first N bytes of each file; with the leading '-', print all but the last N bytes of each file
You can use dd to extract arbitrary chunks of bytes.
For example,
dd skip=1234 count=5 bs=1
would copy bytes 1235 to 1239 from its input to its output, and discard the rest.
To just get the first five bytes from standard input, do:
dd count=5 bs=1
Note that, if you want to specify the input file name, dd has old-fashioned argument parsing, so you would do:
dd count=5 bs=1 if=filename
Note also that dd verbosely announces what it did, so to toss that away, do:
dd count=5 bs=1 2>&-
or
dd count=5 bs=1 2>/dev/null
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.
head:
head - output the first part of files
head [OPTION]... [FILE]...
Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-c, --bytes=[-]N
print the first N bytes of each file; with the leading '-', print all but the last N bytes of each file
you could also grep the line out and then cut it like for instance:
grep 'text' filename | cut -c 1-5
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
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.
You can use dd to extract arbitrary chunks of bytes.
For example,
dd skip=1234 count=5 bs=1
would copy bytes 1235 to 1239 from its input to its output, and discard the rest.
To just get the first five bytes from standard input, do:
dd count=5 bs=1
Note that, if you want to specify the input file name, dd has old-fashioned argument parsing, so you would do:
dd count=5 bs=1 if=filename
Note also that dd verbosely announces what it did, so to toss that away, do:
dd count=5 bs=1 2>&-
or
dd count=5 bs=1 2>/dev/null
head:
head - output the first part of files
head [OPTION]... [FILE]...
Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-c, --bytes=[-]N
print the first N bytes of each file; with the leading '-', print all but the last N bytes of each file
you could also grep the line out and then cut it like for instance:
grep 'text' filename | cut -c 1-5
Here's a simple script that wraps up using the dd
approach mentioned here:
#!/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
you could also grep the line out and then cut it like for instance:
grep 'text' filename | cut -c 1-5
You can use dd to extract arbitrary chunks of bytes.
For example,
dd skip=1234 count=5 bs=1
would copy bytes 1235 to 1239 from its input to its output, and discard the rest.
To just get the first five bytes from standard input, do:
dd count=5 bs=1
Note that, if you want to specify the input file name, dd has old-fashioned argument parsing, so you would do:
dd count=5 bs=1 if=filename
Note also that dd verbosely announces what it did, so to toss that away, do:
dd count=5 bs=1 2>&-
or
dd count=5 bs=1 2>/dev/null
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 '??? µp??? ?a µ??? sa?s???t???;\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 '??? µp??? ?a µ??? sa?s???t???;\n' | \
$ cut -c 1 | \
$ tr '[:upper:]' '[:lower:]'
p
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}).*$/\1/' -e q
- which is limited to the first line thoughhead -n 1 | grep -E -o '^.{X}'
- which is limited to the first line and chains two commands thoughdd
- which has already been suggested in other answers, but is really cumbersomesed
script with sliding window buffer to handle characters spread over multiple lines, but that is probably more cumbersome/fragile than just using something like dd
If your tr
doesn't handle character-classes with variable-byte encodings correctly you could try:
sed -E -e 's/[[:upper:]]/\L&/g
(GNU-specific)head or tail can do it as well:
head -c X
Prints the first X bytes (not necessarily characters if it's a UTF-16 file) of the file. tail will do the same, except for the last X bytes.
This (and cut) are portable.
head -Line_number file_name | tail -1 |cut -c Num_of_chars
this script gives the exact number of characters from the specific line and location, e.g.:
head -5 tst.txt | tail -1 |cut -c 5-8
gives the chars in line 5 and chars 5 to 8 of line 5,
Note: tail -1
is used to select the last line displayed by the head.
You can use dd to extract arbitrary chunks of bytes.
For example,
dd skip=1234 count=5 bs=1
would copy bytes 1235 to 1239 from its input to its output, and discard the rest.
To just get the first five bytes from standard input, do:
dd count=5 bs=1
Note that, if you want to specify the input file name, dd has old-fashioned argument parsing, so you would do:
dd count=5 bs=1 if=filename
Note also that dd verbosely announces what it did, so to toss that away, do:
dd count=5 bs=1 2>&-
or
dd count=5 bs=1 2>/dev/null
Here's a simple script that wraps up using the dd
approach mentioned here:
#!/usr/bin/env bash
function show_help()
{
IT="
extracts characters X to Y from stdin or FILE
usage: X Y {FILE}
e.g.
2 10 /tmp/it => extract chars 2-10 from /tmp/it
EOF
"
echo "$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
Source: Stackoverflow.com