CODEWITHSUNDEEP
awkwhitespacegsubremoving-whitespace
user1194552
user1194552

Reputation: 151

How to remove leading and trailing whitespaces?

I'm using awk '{gsub(/^[ \t]+|[ \t]+$/,""); print;}' in.txt > out.txt to remove both leading and trailing whitespaces.

The problem is the output file actually has trailing whitespaces! All lines are of the same length - they are right padded with spaces.

What am I missing?

UPDATE 1

The problem is probably due to the the fact that the trailing spaces are nor "normal" spaces but \x20 characters (DC4).

UPDATE 2

I used gsub (/'[[:cntrl:]]|[[:space:]]|\x20/,"") an it worked. Two strange things:

  1. Why isn't \x20 considered a control character?

  2. Using '[[:cntrl:][:space:]\x20 does NOT work. Why?

Upvotes: 15

Views: 42329

Answers (4)

Chris Koknat
Chris Koknat

Reputation: 3451

Perl could be used:

perl -lpe 's/^\s*(.*\S)\s*$/$1/' in.txt > out.txt

s/foo/bar/ substitute using regular expressions
^ beginning of string
\s* zero or more spaces
(.*\S) any characters ending with a non-whitespace. Capture it into $1
\s* zero or more spaces
$ end of string

Upvotes: 0

kev
kev

Reputation: 161674

This command works for me:

$ awk '{$1=$1}1' file.txt

Upvotes: 27

oHo
oHo

Reputation: 54561

Your code is OK for me.
You may have something else than space and tabulation...
hexdump -C may help you to check what is wrong:

awk '{gsub(/^[ \t]+|[ \t]+$/,""); print;}' in.txt | hexdump -C | less

UPDATE:

OK you identified DC4 (there may be some other control characters...)
Then, you can improve your command:

awk '{gsub(/^[[:cntrl:][:space:]]+|[[:cntrl:][:space:]]+$/,""); print;}' in.txt > out.txt

See awk manpage:

[:alnum:] Alphanumeric characters.
[:alpha:] Alphabetic characters.
[:blank:] Space or tab characters.
[:cntrl:] Control characters.
[:digit:] Numeric characters.
[:graph:] Characters that are both printable and visible. (A space is printable, but not visible, while an a is both.)
[:lower:] Lower-case alphabetic characters.
[:print:] Printable characters (characters that are not control characters.)
[:punct:] Punctuation characters (characters that are not letter, digits, control characters, or space characters).
[:space:] Space characters (such as space, tab, and formfeed, to name a few).
[:upper:] Upper-case alphabetic characters.
[:xdigit:] Characters that are hexadecimal digits.

Leading/Trailing 0x20 removal

For me the command is OK, I have tested like this:

$ echo -e "\x20 \tTEXT\x20 \t" | hexdump -C
00000000  20 20 09 54 45 58 54 20  20 09 0a                 |  .TEXT  ..|
0000000b
$ echo -e "\x20 \tTEXT\x20 \t" | awk '{gsub(/^[[:cntrl:][:space:]]+|[[:cntrl:][:space:]]+$/,""); print;}' | hexdump -C
00000000  54 45 58 54 0a                                    |TEXT.|
00000005

However if you have 0x20 in the middle of your text
=> then it is not removed.
But this is not your question, isn't it?

Upvotes: 5

Michael J. Barber
Michael J. Barber

Reputation: 25042

Your files probably have Windows line endings. That means that they end with \r\n, so matching a sequence of tabs and spaces at the end of the line won't work -- awk tries to match all the tabs and spaces that come after the \r. Try running the file through tr -d "\r" before sending it to awk.

Upvotes: 1

Related Questions