How to remove all newlines from all .txt files in a folder, using UNIX tools?

Question

I got about 300 (.txt) files in a folder with "normal text" formatted with /n's. I want all text in these files, to be in the first line, because a program in my pipeline requires that.

Exampel:

(IS:)
GTCGCAGCCG
TCGGCTCGGA
TCTCGGCCTC

(SHOULD BE:)
GTCGCAGCCGTCGGCTCGGATCTCGGCCTC

If I could overwrite them all, with file names staying the same, that would be convenient. I don't want to crack out python yet, is there an easy UNIX tool / command line approach?

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I was here before: How do I remove newlines from a text file?

But how to do that for all 300 files in my folder? If i use tr -d '\n' < *.txt it tells me: "bash: *.txt: ambiguous redirect"

Answer 1

You need a shell loop to process each file in turn. Note that ed is a better choice than tr, as it is designed to work with files, not streams.

for f in *.txt; do
    printf '%%j\nwq\n' | ed "$f"
done

%j is the ed command to join all lines in the buffer; the %% is necessary here to make printf output a literal %. wq is the command to write changes back to the file and quite. (The q is optional, as ed will exit after the end of its script anyway.)