[bash] Concatenating multiple text files into a single file in Bash

Be careful, because none of these methods work with a large number of files. Personally, I used this line:

for i in $(ls | grep ".txt");do cat $i >> output.txt;done

EDIT: As someone said in the comments, you can replace $(ls | grep ".txt") with $(ls *.txt)

EDIT: thanks to @gnourf_gnourf expertise, the use of glob is the correct way to iterate over files in a directory. Consequently, blasphemous expressions like $(ls | grep ".txt") must be replaced by *.txt (see the article here).

Good Solution

for i in *.txt;do cat $i >> output.txt;done