CODEWITHSUNDEEP
linuxsed
Mbola
Mbola

Reputation: 9

Linux remove whitespace first line

i have the file virt.txt contains:

0302        000000       23071SOCIETY              117
0602        000000000000000001 PAYMENT              BANK

I want to remove 3 whitespaces from 6th to 8th column to the first line only.

I do:

 sed '1s/[[:blank:]]+[[:blank:]]+[[:blank:]]//6' virt.txt

it'KO please help

Upvotes: 0

Views: 358

Answers (1)

tripleee
tripleee

Reputation: 189387

Your regex would consume all the available blanks from a sequence of three or more (in a quite inefficient way) and replace the sixth occurrence of that. Because your first input line does not contain six or more separate stretches of three or more whitespace characters, it actually did nothing. But you can in fact use sed to do exactly what you say you want:

sed '1s/^\(.....\)   /\1/' virt.txt

(or for convenience, if you have sed -E or the variant sed -r which works on some platforms, but neither of these is standard):

sed -E '1s/^(.{5}) {3}/\1/' virt.txt  # -E is not portable

The parentheses capture the first five characters into a back reference, and we then use the first back reference \1 as the replacement string, effectively replacing only the text which matched outside the parentheses.

If your sed supports the -i option, you can use that to modify the file directly; but this is also not standard, so the most portable solution is to write the result to a new file, then move it back on top of the original file if you want to replace it.

sed is convenient if you are familiar with it, but as you are clearly not, perhaps a better approach would be to use a different language, ideally one which is not write-only for many users, like sed.

If you know the three characters will always be spaces, just do a static replacement.

awk 'NR==1 { $0 = substr($0, 1, 5) substr($0, 9) } 1' virt.txt

On the first line (NR is the current input line number) replace the input line $0 with a catenation of the substrings on both sides of the part you want to cut.

For a simple replacement like that, you can also use basic Unix text manipulation utilities, though it's rather inefficient and inelegant:

head -n 1 virt.txt | cut -c1-5,9- >newfile.txt
tail -n +2 virt.txt >>newfile.txt

If you need to check that the three characters are spaces, the Awk script only needs a minor tweak.

awk 'NR==1 && /^.{5} {3}/ { $0 = substr($0, 1, 5) substr($0, 9) } 1' virt.txt

You should vaguely recognize the regex from above. Awk is less succinct, but as a consequence also quite a lot more readable, than sed.

Upvotes: 2

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