Bash Script: Appending Text at the Last Character of Specific Line of a File

Bash script: Appending text at the last character of specific line of a file

Try this:

sed -i "/^MYVERSION=/ s/\$/$VERSION/" myfile.txt

The idea is that it finds a line that starts with MYVERSION= and then replaces the end of that line with the contents of the $VERSION environment variable.

Edit: originally I wasn't sure if the first $ needed to be escaped, but @sehe's comment and its upvoters convinced me that it does.

How to append a string at end of a specific line in a file in bash

Using sed and the pattern described:

sed '/192.168.1.2/s/$/ myalias/' file

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Using sed and a specific line number:

sed '2s/$/ myalias/' file

bash append text with special character and newline to file at specific line

The problem you are having is the text contained in print_config has unescaped newlines in the file. Specifically you are attempting multi-line insert of:

@ReactMethod
public void printBarCode(String str, int nType, int nWidthX, int nHeight,
          int nHriFontType, int nHriFontPosition) {
    byte[] command = PrinterCommand.getBarCodeCommand(str, nType, nWidthX, nHeight, nHriFontType, nHriFontPosition);
    sendDataByte(command);
}

You cannot do that without preceding each newline with a '\' character. From man sed you have "i \ text Insert text, which has each embedded newline preceded by a backslash."

Instead, you may be better served by saving the contents above to a temporary file and then using the r filename command to "Append text read from filename". In your case you would have:

sed -i '436r tempfile' file_to_modify

That would read the contents of tempfile into file_to_modify at line 436 without having to modify the text to escape each newline with a backslash.

Append text to the last line of a file in unix

You could go with dd and notrunc (tested on Linux 4.12):

printf ":" | dd of=file conv=notrunc bs=1 seek=$(( $(stat -c "%s" file) - 1))

How to append a character at the end of a specific line in a loop?

TL;DR:

$: c='!'
$: sed "s#\$# s/\$/ $c/#" fibs >script
$: sed -i "$(<script)" infile

Broken out -

A file of line numbers:

$: cat fibs
1
2
3
5
8
13
21

a file to be edited:

$: cat infile
  1 a
  2 b
  3 c
  4 d
  5 e
  6 f
  7 g
  8 h
  9 i
 10 j
 11 k
 12 l
 13 m
 14 n
 15 o
 16 p
 17 q
 18 r
 19 s
 20 t
 21 u
 22 v
 23 q
 24 x
 25 y
 26 z

3 steps -- first set your character variable if you're using one.

$: c='!'

Then make a script from the line number file -

$: sed "s#\$# s/\$/ $c/#" fibs >script

which creates:

$: cat script
1 s/$/ !/
2 s/$/ !/
3 s/$/ !/
5 s/$/ !/
8 s/$/ !/
13 s/$/ !/
21 s/$/ !/

It's a simple sed to add a sed substitution command for each line number, and sends the resulting script to a file. A few tricks here include using double-quotes to allow the character embedding, and #'s to allow the replacement text to include /'s without creating leaning-toothpick syndrome from all the backslash quoting.

Then run it against your input -

$: sed -i "$(<script)" infile

Which does the work. That pulls the script file contents in for sed to use, generating:

  1 a !
  2 b !
  3 c !
  4 d
  5 e !
  6 f
  7 g
  8 h !
  9 i
 10 j
 11 k
 12 l
 13 m !
 14 n
 15 o
 16 p
 17 q
 18 r
 19 s
 20 t
 21 u !
 22 v
 23 q
 24 x
 25 y
 26 z

Let me know if you want to tweak it.

Bash: append text to last line of file

sed '${s/$/%/}' file

Appending a new line to a file, checking whether last character is a newline character or not in Bash

You can use:

x=$(tail -c 1 aFile.txt)
if [ "$x" != "" ]
then echo >> aFile.txt
fi
echo "some line of text" >> aFile.txt

The $(...) operator removes the trailing newline from the output of the command embedded in it, and the tail -c 1 command prints the last character of the file. If the last character is not a newline, then the string "$x" won't be empty, so append a newline to the file before appending the new line of text.

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