Output concatenation of file contents and custom text into a new file

Question

Sorry for a noob question but, well, I am a noob, so...

Given two files, say file1 with content, say, text1 and file2 with content text2, I want to create a new file file3 with content text1newtextinbetweentext2. I would expect some command like

cat file1 (dontknowwhat "newtextinbetween") file2 > file3

Is there some dontknowwhat that would do what I want? If not, what is the optimal way to do it?

terdon · Answer 1 · 2020-12-04T08:58:36.777

7

Here are two ways:

Group the commands

 $ { cat file1; echo "newtextinbetween"; cat file2; } > file3
 $ cat file3
 text1
 newtextinbetween
 text2

Use a subshell

 $ ( cat file1; echo "newtextinbetween"; cat file2 ) > file3
 $ cat file3
 text1
 newtextinbetween
 text2

Use command substitution

 $ printf '%s\nnewtextinbetween\n%s\n' "$(cat file1)" "$(cat file2)" > file3
 $ cat file3
 text1
 newtextinbetween
 text2

If you don't want the newlines between each block, you can do:

 $ printf '%snewtextinbetween%s\n' "$(cat file1)" "$(cat file2)" > file3
 $ cat file3
 text1newtextinbetweentext2

edited Dec 04 '20 at 08:58

answered Dec 03 '20 at 17:03

terdon

242,166

3

... or (bash/zsh/ksh) even printf '%snewtextinbetween%s\n' "$(<file1)" "$(<file2)" if you're not a cat lover – steeldriver Dec 03 '20 at 17:11
Excellent, thanks! The last version is precisely what I want. Just one detail: say, this newtextinbetween was the value of some variable WHATTOINSERT; would something like printf '%s($WHATTOINSERT)%s\n'... work then? – მამუკა ჯიბლაძე Dec 03 '20 at 17:14
1

@მამუკაჯიბლაძე no, variables aren't expanded inside single quotes, just add another %s like this: printf '%s%s%s\n' "$(cat file1)" "$WHATTOINSERT" "$(cat file2)" > file3 – terdon Dec 03 '20 at 18:36
Thank you! Very nice. – მამუკა ჯიბლაძე Dec 03 '20 at 19:49
3

Could use { to group instead of (. – rowboat Dec 04 '20 at 00:35
1

@rowboat I could and I should, there's no need for a subshell. Thanks! – terdon Dec 04 '20 at 08:58

Bashful Thinking · Accepted Answer · 2020-12-03T17:29:02.667

5

Another way to do this is to use process substitution:

cat file1 <(echo "newtextinbetween") file2 > file3

Edit: If you don't what echo to add a line break use echo -n instead.

edited Dec 03 '20 at 17:29

answered Dec 03 '20 at 17:24

Bashful Thinking

78
5

Wow this looks even sleeker! But how about avoiding newline between newtextinbetween and the contents of file2? – მამუკა ჯიბლაძე Dec 03 '20 at 17:26
Fantastic! Had to behave ungraciously and move my acceptance from the previous answer to this one. Essentially because what I asked there is very easy to do here, just do cat file1 <(echo -n $WHATEVER) file2 > file3 – მამუკა ჯიბლაძე Dec 03 '20 at 17:32
4

@მამუკაჯიბლაძე nothing ungracious about it at all! You should always accept the answer you personally find most useful. Just note that a safer/more portable way would be cat file1 <(printf '%s' "newtextinbetween") file2 > file3 since not all echo implementations understand -n (see Why is printf better than echo?). – terdon Dec 03 '20 at 18:37
@terdon Thanks! Good to know. In my case -n worked, I just checked it, so... – მამუკა ჯიბლაძე Dec 03 '20 at 19:48

Output concatenation of file contents and custom text into a new file

2 Answers2