Unable to refer to a parameter in Bash

Question

I want to put TextA to the beginning of TextB by

cat TextA A TextB

The problem is that I do not know how to refer to the first and second parameters, that is TextA and TextB in the following script called A:

  #!/bin/bash

  cat TextA > m1
  cat TextB > m2
  cat m1 m2 > TextB

where m1 and m2 are temporary files.

How can you refer to the two files in the shell script?

Answer 1

you could just use append (>>)

cat TextB >> TextA

result is that TextA precedes text TextB in TextA

Answer 2

You can use $0, $1, $2 etc. to refer to the variables in the script.

$0 is the name of the script itself
$1 is the first parameter
$2 is the second parameter
and so on

For instance, if you have this command:

a A1 A2

Then inside a you'll have:

$0 = a
$1 = A1
$2 = A2

Answer 3

In a bash script is the first parameter is $1, the second is $2 and so on.

If you want a default value for example the third parameter you can use:

var=${3:-"default"}

Answer 4

Looks like you can just do the following:

TextA="text a"
TextB="text b"
echo "$TextA $TextB" > file1

Or use the append (>>) operator.

Answer 5

I would do the following:

#!/bin/bash

if [ $# -ne 2 ]
then
  echo "Prepend file with copyright notice"
  echo "Usage: `basename $0` <copyright-file> <mainfile>"
  exit 1
fi

copyright=$1
mainfile=$2

cat $mainfile > /tmp/m.$$
cat $copyright /tmp/m.$$ > $mainfile

#cleanup temporary files
rm /tmp/m.$$ /tmp/m2.$$

Answer 6

I am surprised that nobody suggests the following result

cat TextA TextB | tee > TextB

This way, you can avoid the hassle of creating a temporary file.