Carriage return issue

Question

I have this in a bash script

DAY2="20130605"<Cr>
echo  "This is yesterday date:"$DAY2"end"

Why is the output the following? It seems as though there is a carriage return in DAY2 but where is it coming from?

ends is yesterday date:20130605

Answer 1

Carriage return puts the cursor back to the beginning of the line. Your output string is:

    This is yesterday date:20130605<Cr>end

Except, when the terminal hits the <Cr> it returns the cursor to the beginning of the line and overwrites the characters that are there.

In other words, "Thi" gets replaced with "end", producing:

    ends is yesterday date:20130605

To do what you appear to be trying to do your script should look something like this:

   variable="text"
   echo "Some sentence $variable"

Which will output

   Some sentence text

IF there are stray carriage returns they should show up as ^M in vi (as Bruce said)

Solution 1

The best way to remove carriage returns or other non-printing characters is with the tr command with the -d option, which deletes any instance of a single character, with \r which is the escape sequence for carriage return:

    tr -d '\r'

This will remove all carriage returns. Run it on the script to remove all instances of carriage returns, then overwrite the original script file:

    tr -d '\r' yourscript.bash > temp
    mv temp yourscript.bash

Solution 2

or while in vi with the script open enter:

    :%s/\r//g
    :wq

To remove the carriage returns within the document then save it.

Answer 2

Assuming <Cr> represents a carriage return, remove the carriage return from the end of the first line. Here's a one-liner to do it for you:

sed -i '1s/\r//' script.sh

To see the carriage returns in your script, run the following.

od -c script.sh | grep --color=yes '\r'

Answer 3

Use vi or vim to look at the bash script in question. You should see any stray carriage returns as '^M' (caret, em) two-character sequences. Use hjkl to move cursor over the carriage returns, hit 'x' to delete them, then ":wq" to get out of vi.

My guess would be that a stray carriage return got into the file when someone moved the file to a Windows machine, edited it with Notepad or Wordpad, and then moved it back to linux.

Answer 4

In shell scripts, CR is an ordinary character, not whitespace like in many other languages. That line DAY2="20130605"<Cr> sets DAY2 to a 9-character string, it's equivalent to DAY2=$'20130605\r'. The echo line is equivalent to echo $'This is yesterday date:20130605\rend'. The CR character ($'\r') moves the cursor to the beginning of the line, thus (¡ indicates the cursor location):

This is yesterday date:¡               #after printing up to date:
This is yesterday date:20130605¡       #after printing up to 20130605
¡This is yesterday date:20130605       #after printing the CR
end¡s is yesterday date:20130605       #after printing end

Remove the CR from the script.

Answer 5

Exactly how that carriage return came to be is hard to say.

If the script was generated by another script or an application it could be a bug or intended mishap.

Most likely you or whomever edited the file has unintentionally pressed a key combination causing CR to be inserted.

Examples:

• vim : Ctrl-v Ctrl-m
• emacs: Ctrl-q Ctrl-m
• And many others.

There are other characters that can cause trouble as well, e.g. no-break-space in code etc. This usually cause weird bugs when running scripts or compiling code.

I normally use vim and frequently set (have a key-combination to toggle it):

match Error /[^ -~\t]/

That is: highlight everything but <space> to ~ in ASCII and tab with Error, typically white on red etc.

For code files I usually have this is set on by default.

---

In the terminal carriage return normally causes the cursor to move to start of line, thus any print after it is overwriting any existing text on that line until a line feed comes along.

E.g.:

#!/bin/bash

for i in {1..100}; do
    printf "We are now at %3d%%\r" "$i"
    sleep .1
done

printf "\nAll done.\n"

\r, when using printf result in <CR> or Carriage Return.
\n, when using printf result in <LF> or Line Feed.