Reading from a text file and printing the words character by character at a time

Question

I would like to write a program that reads from a text file and prints in Terminal the words of that file character by character every one second.

For example, in a text file log.txt let's say I have this sentence:

I love Unix but I don't know programming.

I would like the code to read the previous sentence and print the letters, the spaces one by one every second.

Sergiy Kolodyazhnyy · Answer 1 · 2018-09-08T21:33:41.560

9

Goro's answer will work, but it should be noted that command substitution removes trailing newlines as specified by POSIX standard. Thus it may not be desirable where you want to actually iterate over all charactes, even non-printable ones. Another issue is that C-style for loop is used in bash and ksh93, but not in standard (aka POSIX-comliant ) /bin/sh. The ${variable:index:offset} form of parameter expansion is also type of bashism and not specified by POSIX definitions of parameter expansion (though supported by ksh93 and zsh).

Nonetheless, there's a way to iterate over all characters in file portably and in a far more practical way. That's to use awk:

# all characters on the same line
$ awk '{for(i=1;i<=length;i++){ printf "%c",substr($0,i,1); system("sleep 1");}; print}' input.txt

# all characters on separate lines
$ awk '{for(i=1;i<=length;i++){ print substr($0, i, 1); system("sleep 1"); }}' input.txt

With this command substr() and system() are both specified in POSIX awk and will in fact iterate over all characters.

edited Sep 08 '18 at 21:33

answered Sep 08 '18 at 21:12

Sergiy Kolodyazhnyy

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1

@Goro Already added a comment about that, see the edit – Sergiy Kolodyazhnyy Sep 08 '18 at 21:15
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@don_crissti I need to find a better phrase than "bashism" because I always get `ksh` and `zsh` mentioned. Can we start using something like `{ba,k,z}sh` maybe ? :) – Sergiy Kolodyazhnyy Sep 08 '18 at 21:33
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I think just mentioning non-posix or non-standard would do... – don_crissti Sep 08 '18 at 21:33
@don_crissti non-posix adds another level of ambiguity because POSIX mostly was based on `ksh` and Bourne shell, and bash has `--posix` flag and supoorts most of the POSIX features. Idk, there's gotta be a better way to phrase it – Sergiy Kolodyazhnyy Sep 09 '18 at 00:28
I don't find it ambiguous tbh... Also, you seem to be contradicting yourself: your answer says "_not specified by POSIX_" but you're saying that using "_non-posix_" is ambiguous... How is "_non-posix_" different than "_not specified by POSIX_" ? Anyway, feel free to use any term/phrase you find appropriate, my point was against _bashism_ - which is the wrong term considering the fact that `bash` copied a lot from `ksh` (and even `zsh); most features that some people call _bashisms_ have originated in other shells (and, obviously, are supported in those shells too). – don_crissti Sep 09 '18 at 10:09

score 3 · Answer 2 · 2018-09-08T21:08:39.853

3

You can do this

var=$(cat log.txt)
for (( i=0; i<${#var}; i++ )); do
 sleep 1 | echo -ne "${var:$i:1}"
done
echo ""

edited Sep 08 '18 at 21:08

answered Sep 08 '18 at 20:10

thk for quick answr. this is wht i want but why it priunt on the same line ike this `I love Unix but I don't know programming.[zahi@sonar]$, how print on separate line? – Zahi Sep 08 '18 at 20:30
Ah, please see my revisions – Sep 08 '18 at 20:32

score 3 · Answer 3 · answered Sep 08 '18 at 22:46

3

With bash or ksh93 you can read single characters using the shell's built-in read command:

while IFS= read -r -n 1 c; do 
  printf '%c' "$c"
  sleep 1
done < log.txt
printf '\n'

answered Sep 08 '18 at 22:46

steeldriver

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score 1 · Answer 4 · answered Sep 09 '18 at 03:32

Here's a Python solution:

python -c "from time import sleep
with open('/tmp/file.txt') as f:
 for line in f:
  for c in line:
   print(c, end='', flush=True);sleep(1);"

You should just be able to paste that on the command line and change the name of the input file.

score 0 · Answer 5 · answered Sep 09 '18 at 19:42

You could do this with Perl as shown:

perl -pe 'BEGIN{$/=\1;$|=1;} sleep 1' log.txt

-p will autoprint the current record before fetching the next.
$/=\1 will make perl read the input stream a byte at a time, and assuming the characters are a byte sized.
$|=1 will output is buffered.

Reading from a text file and printing the words character by character at a time

5 Answers5