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I have hundreds of *.txt files which have a common format.
I can insert a comma at a specific position in one file, how can I generalize the below code to apply this operation at several places for all *.txtfiles in the directory?
sed -i 's/^\(.\{4\}\)/\1,/' blank.txt
For example inserting commas at positions 4, 8, 22 etc.
Something like this perhaps?
for i in *.txt; do
sed -i 's/^\(.\{4\}\)/\1,/' $i
done
In a general way, you can just do:
sed 's/./&,/4' <in >out
That will append a comma on output to the 4th character of all input lines with at least that many characters.
And, if you'll take my advice, you should generally not use the -i switch to any sed which offers one.
-i? Without it the process of changing a file is mv file file.new;sed '...' < file.new > file;rm file.new which is cumbersome and unsafe against multiple users. In place editing has the additional advantage that given a small enough file (under the system default buffer size, which is quite large for text files) the edit is atomic in respect to other users)
-i doesn't edit the file but replaces it. It is especially a problem for multi-user systems, because, counterintuitively, the file's permissions don't matter and only it's parent directory's permissions do. -i alters metadata - maybe even ownership. The mv file.new file.old command you detail is exactly what sed does, only it doesn't advertise that fact, nor does it respect such norms as $TMPDIR nor even ~ and just writes to the read file's parent directory while it works, before mv it over the read file at exit.
sed -i does retain some metadata, under (what I believe is) acceptable measures given specific conditions. For specific details, see this answer - unix.stackexchange.com/a/146054/4323 .
Start from the rightmost one:
sed -i 's/./&,/22;s/./&,/8;s/./&,/4' ./*.txt
Otherwise, the first substitution would affect the offset for the second. You can always account for it though:
sed -i 's/./&,/4;s/./&,/9;s/./&,/24' ./*.txt
When you mention 'at positions 4,8 and 22', sed means 'one after positions 3,7 and 21'. You want to insert and keep the existing text as is.
This?:
sed -i -r "s/^(.{3})/\1,/;s/^(.{7})/\1,/;s/^(.{21})/\1,/" $(dirname "$0")/blank.txt
-i = --in-place aka change directly in the existing file, -r = regular expression, \1 = refers to the 'group' between parenthesis, $(dirname "$0") = to stay in the current dir
A similar sed-use when you want to e.g. set tabs instead of spaces at certain positions in a file with lines seperated by single spaces:
sed -i -r "s/^(.{10})./\1\t/;s/^(.{20})./\1\t/;s/^(.{30})./\1\t/" $(dirname "$0")/blank.txt
Substitutes the characters (in this case single spaces) at position 11, 21 and 31 by a tab. The spaces within the created columns stay untouched.
You can still get the impression that this doesn't align/display your columns well in your text-editor. The coded tabs aren't wrong, but often you need to adapt the tab-setting in the text-editor preferences. E.g. Geany -> Preferences -> Editor -> Indentation -> Tabs width 8 instead of 4.
(The latter somewhat aside your original question...)
s/^\(.\{4\}\)/\1,/. The fact that you say s/^(.{3})/\1,/ suggests that you’re misunderstanding the question. (2) Since the question already mentions sed -i, it seems unnecessary for you to explain what it does. (3) Why are you talking about tabs?
Jul 15, 2022 at 3:09
sed s/^...../&,/ /path/to/filewill do it.s/^\(.\{4\}\)/\1,/tos/^.\{4\}/&,/and still be usable as anexcommand or withinvi. (Of course it could be further simplified tos/./&,/4for use insed.)