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I'm stuck - piping a text file like this:

cat file1.txt | sed '/^[0-9].*[0-9]$/d' > file2.txt

This regex catches the lines in a text editor, and it works when I use it to delete all blank lines in the same file, so no problem with (Linux/Windows) newline format I guess.

I wonder why this does not delete those lines, or how this can be done otherwise?

  • So what is your problem? – cuonglm Nov 18 '15 at 12:17
  • @cuonglm: sorry for not being clear enough; edited now. – Sadi Nov 18 '15 at 12:24
  • I don't understand the question, the sed command works. But I don't understand your second sentence. "This regex catches the lines in a text editor" what text editor? "it works when I use it to delete all blank lines" blank lines? I thought its about begin and end with a digit? You may need to give example input and desired output. – chaos Nov 18 '15 at 12:43
  • Has the source data file come from a Windows system? If so, [0-9] will not match the last character on a line. – roaima Nov 18 '15 at 13:14
  • @chaos ; no the sed command above doesn't work although I can search and replace / delete lines using the same regex, i.e. ^[0-9].*[0-9]$ in a text editor like gedit or kkedit. – Sadi Nov 18 '15 at 13:51
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Some extra notes:

sed '/^[0-9].*[0-9]$/d'

Would fail to delete the lines that contain a single digit (even though they start and end in a digit).

Also note that in many locales, [0-9] matches more than the 0123456789 digits. If you want to match on those only, you'd need [0123456789] or [[:digit:]].

The more obvious command to filter lines based on a pattern is grep.

cat is the command to concatenate. It makes little sense to concatenate a single file.

Here, to address all those and ignore any leading or trailing spacing characters (like the MS-DOS trailing carriage returns in your input), you could do:

<file.txt.in grep -e '^[[:space:]]*[^[:digit:][:space:]]' \
                  -e '[^[:digit:][:space:]][[:space:]]*$' \
                  -e '^[[:space:]]*$' > file.txt.out

(that is return the lines that start or end in a non-digit (past the leading whitespace, or before the trailing whitespace), or are all whitespace.

Or:

<file.txt.in grep -vx '[[:space:]]*[[:digit:]]\(.*[[:digit:]]\)\{0,1\}[[:space:]]*' > file.txt.out

Or the same with EREs:

<file.txt.in grep -vxE '[[:space:]]*[[:digit:]](.*[[:digit:]])?[[:space:]]*' > file.txt.out

That is, filter out (with -v) the lines that start with a digit optionally followed by the rest a line ending in a digit, allowing whitespace at the start and ned.

Those ones could however fail to remove lines like 8xx<non-character>yy8 where <non-character> is a sequence of bytes that don't form a valid character in the current locale. But in any case, you can't expect much portably for this kind of line that is not valid text.

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If

cat file1.txt | sed '/^\s*$/d' > file2.txt

works, but

cat file1.txt | sed '/^[0-9].*[0-9]$/d' > file2.txt

doesn't (although one would expect to work like the former);

considering that input file might include Windows carriage returns, then it might be safer to use this command instead:

cat file1.txt | sed '/^[0-9].*[0-9]\(\r\|$\)/d' > file2.txt

This should work in all cases, including lines ending with Linux or Windows carriage return.

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  • 1
    [$] is a literal dollar sign, so the line 1$x would be deleted by this command. – Benjamin W. Jan 22 '19 at 14:29
  • @BenjaminW. thanks for the warning! Any suggestions for adding \r without using two commands? – Sadi Jan 23 '19 at 7:06
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    Something like \(\r\|$\) (or (\r|$) for sed -E) maybe? – Benjamin W. Jan 23 '19 at 14:45
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    Note that \s, \r and \| are non-standard (originally GNU) extensions. – Stéphane Chazelas Jan 24 '19 at 10:05

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