R – Problem in using Sed to remove leading and trailing spaces

linuxmatchingpattern matchingregexunix

I am using the following code to remove both leading and tailing spaces from all lines of a file A.txt

sed 's/^[ \t]*//;s/[ \t]*$//' ./A.txt > ./B.txt

The problem occurs on the lines where there is a t in the beginning or at the end. So say for example, the original line that starts with the string "timezone" becomes "imezone"

Can you please tell me what is happening here? and also if there is a known solution to the problem.

Thanks in advance.

Best Answer

Some older versions of sed don't understand C-style escape characters such as \t and treat that as two characters, '\' and 't'. You can avoid the problem by using a literal tab character -- if you're typing this directly into the shell, type Ctrl+V Tab.

Explanation:

du: Disk Usage

-s: Display a summary for each specified file. (Equivalent to -d 0)

-h: "Human-readable" output. Use unit suffixes: Byte, Kibibyte (KiB), Mebibyte (MiB), Gibibyte (GiB), Tebibyte (TiB) and Pebibyte (PiB). (BASE2)

Java how to replace 2 or more spaces with single space in string and delete leading and trailing spaces

Try this:

String after = before.trim().replaceAll(" +", " ");

No `trim()` regex

It's also possible to do this with just one replaceAll, but this is much less readable than the trim() solution. Nonetheless, it's provided here just to show what regex can do:

    String[] tests = {
        "  x  ",          // [x]
        "  1   2   3  ",  // [1 2 3]
        "",               // []
        "   ",            // []
    };
    for (String test : tests) {
        System.out.format("[%s]%n",
            test.replaceAll("^ +| +$|( )+", "$1")
        );
    }

There are 3 alternates:

^_+ : any sequence of spaces at the beginning of the string
- Match and replace with $1, which captures the empty string
_+$ : any sequence of spaces at the end of the string
- Match and replace with $1, which captures the empty string
(_)+ : any sequence of spaces that matches none of the above, meaning it's in the middle
- Match and replace with $1, which captures a single space

Best Answer

Related Solutions

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Explanation:

Java how to replace 2 or more spaces with single space in string and delete leading and trailing spaces

See also

No trim() regex

See also

Related Topic

No `trim()` regex