Bash - How to Print Multi Line Strings (With '\N') Using Printf

Bash - How to print multi line strings (with '\n') using printf

Quoting the variable should do the trick. In your example, however, you are getting double newlines.

printf "$text_content"

Multi-line string with extra space (preserved indentation)

Heredoc sounds more convenient for this purpose. It is used to send multiple commands to a command interpreter program like ex or cat

cat << EndOfMessage
This is line 1.
This is line 2.
Line 3.
EndOfMessage

The string after << indicates where to stop.

To send these lines to a file, use:

cat > $FILE <<- EOM
Line 1.
Line 2.
EOM

You could also store these lines to a variable:

read -r -d '' VAR << EOM
This is line 1.
This is line 2.
Line 3.
EOM

This stores the lines to the variable named VAR.

When printing, remember the quotes around the variable otherwise you won't see the newline characters.

echo "$VAR"

Even better, you can use indentation to make it stand out more in your code. This time just add a - after << to stop the tabs from appearing.

read -r -d '' VAR <<- EOM
    This is line 1.
    This is line 2.
    Line 3.
EOM

But then you must use tabs, not spaces, for indentation in your code.

How to output a multiline string in Bash?

Here documents are often used for this purpose.

cat << EOF
usage: up [--level <n>| -n <levels>][--help][--version]

Report bugs to: 
up home page:
EOF

They are supported in all Bourne-derived shells including all versions of Bash.

How to concatenate multiple lines of output to one line?

Use tr '\n' ' ' to translate all newline characters to spaces:

$ grep pattern file | tr '\n' ' '

Note: grep reads files, cat concatenates files. Don't cat file | grep!

Edit:

tr can only handle single character translations. You could use awk to change the output record separator like:

$ grep pattern file | awk '{print}' ORS='" '

This would transform:

one
two 
three

to:

one" two" three" 

Echo newline in Bash prints literal \n

Use printf instead:

printf "hello\nworld\n"

printf behaves more consistently across different environments than echo.

How to printf multiline output in place?

There are different terminal command sequences for that sort of thing. You might be able to save the cursor position and restore it with:

$ tput sc; printf 'multi\nline\noutput\n'; tput rc; printf '%s' 'overwrite line 1'; echo; echo; echo
overwrite line 1
line
output

For your case, that becomes:

tput sc     # Save cursor position
for i in {1..100}; do
  outp=$(df -h |grep sda)
  printf '%s' "$outp"
  tput rc   # Restore cursor position
done

Note that it is bad practice to use ALL_CAPS for variable names, and also that the variable here is totally unnecessary (unless you wish to retain the data for use later in the script). You could easily do:

for i ...; do
  tput sc
  df -h | grep sda
  tput rc
done

How can I have a newline in a string in sh?

If you're using Bash, you can use backslash-escapes inside of a specially-quoted $'string'. For example, adding \n:

STR=$'Hello\nWorld'
echo "$STR" # quotes are required here!

Prints:

Hello
World

If you're using pretty much any other shell, just insert the newline as-is in the string:

STR='Hello
World'

Bash recognizes a number of other backslash escape sequences in the $'' string. Here is an excerpt from the Bash manual page:

Words of the form $'string' are treated specially. The word expands to
string, with backslash-escaped characters replaced as specified by the
ANSI C standard. Backslash escape sequences, if present, are decoded
as follows:
      \a     alert (bell)
      \b     backspace
      \e
      \E     an escape character
      \f     form feed
      \n     new line
      \r     carriage return
      \t     horizontal tab
      \v     vertical tab
      \\     backslash
      \'     single quote
      \"     double quote
      \nnn   the eight-bit character whose value is the octal value
             nnn (one to three digits)
      \xHH   the eight-bit character whose value is the hexadecimal
             value HH (one or two hex digits)
      \cx    a control-x character

The expanded result is single-quoted, as if the dollar sign had not
been present.

A double-quoted string preceded by a dollar sign ($"string") will cause
the string to be translated according to the current locale. If the
current locale is C or POSIX, the dollar sign is ignored. If the
string is translated and replaced, the replacement is double-quoted.

How does cat EOF work in bash?

This is called heredoc format to provide a string into stdin. See https://en.wikipedia.org/wiki/Here_document#Unix_shells for more details.

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From man bash:

Here Documents

This type of redirection instructs the shell to read input from
the current source until a line
containing only word (with no trailing
blanks) is seen.

All of the lines read up to that point are then used as the
standard input for a command.

The format of here-documents is:

          <<[-]word
                  here-document
          delimiter

No parameter expansion, command substitution, arithmetic expansion, or
pathname expansion is performed on
word. If any characters in word are
quoted, the
delimiter is the result of quote removal on word, and the lines
in the here-document are not expanded.
If word is unquoted, all lines of the
here-document are subjected to parameter expansion, command
substitution, and arithmetic
expansion. In the latter case, the
character sequence \<newline> is
ignored, and \ must be used to quote the characters \, $, and `.

If the redirection operator is <<-, then all leading tab characters
are stripped from input lines and the
line containing delimiter. This
allows here-documents within shell scripts to be indented in a natural fashion.

How do I specify new lines in a string in order to write multiple lines to a file?

It depends on how correct you want to be. \n will usually do the job. If you really want to get it right, you look up the newline character in the os package. (It's actually called linesep.)

Note: when writing to files using the Python API, do not use the os.linesep. Just use \n; Python automatically translates that to the proper newline character for your platform.

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