this post was submitted on 25 Oct 2023
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What is the function for reading text line by line from the command line in batch mode? (alien.top)
submitted 11 months ago by vfclists@alien.top to c/emacs
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I want to write a script to process the contents of a text file line by line, and came across this example on Emacs wiki - https://www.emacswiki.org/emacs/BatchMode

emacs --batch --eval "(while t (print (eval (read))))"

So I adjusted it to emacs --batch --eval "(while t (print (read)))" and the prompt Lisp expression: is always displayed.

─○ emacs --batch --eval "(while t (print (read)))" 
Lisp expression: fdfdfds

fdfdfds
Lisp expression: dsfdsfdfds

Lisp expression: ^C%

When I try a command like cat text1.txt | emacs --batch --eval "(while t (print (read)))" it barfs completely, so read is definitely not the function for this, unless I'm failing to pass some necessary options to it.

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[–] vfclists@alien.top 1 points 11 months ago

I made some progress, with read-from-minibuffer the function I need, however I want to terminate the script and suppress the error information at the end.

─○ cat text1.txt | emacs -batch --eval "(while t (princ (read-from-minibuffer \"\") (terpri)))"

Here is some text
Will it be tripled?

Here is some text
Will it be tripled?

Here is some text
Will it be tripled?
Debugger entered--Lisp error: (end-of-file "Error reading from stdin")
  read-from-minibuffer("")
  (princ (read-from-minibuffer "") (terpri))
  (while t (princ (read-from-minibuffer "") (terpri)))
  eval((while t (princ (read-from-minibuffer "") (terpri))) t)
  command-line-1(("--eval" "(while t (princ (read-from-minibuffer \"\") (terpri)..."))
  command-line()
  normal-top-level()