How to horizontally mirror ascii art? - image-processing

Question

So ... I know that I can reverse the order of lines in a file using tac or a few other tools, but how do I reorder in the other dimension, i.e. horizontally? I'm trying to do it with the following awk script:
{
out="";
for(i=length($0);i>0;i--) {
out=out substr($0,i,1)}
print out;
}
This seems to reverse the characters, but it's garbled, and I'm not seeing why. What am I missing?
I'm doing this in awk, but is there something better? sed, perhaps?
Here's an example. Input data looks like this:
$ cowsay <<<"hello"
_______
< hello >
-------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
And the output looks like this:
$ cowsay <<<"hello" | rev
_______
> olleh <
-------
^__^ \
_______\)oo( \
\/\) \)__(
| w----||
|| ||
Note that the output is identical whether I use rev or my own awk script. As you can see, things ARE reversed, but ... it's mangled.

Answer 1

rev is nice, but it doesn't pad input lines. It just reverses them.
The "mangling" you're seeing is because one line may be 20 characters long, and the next may be 15 characters long. In your input text they share a left-hand column. But in your output text, they need to share a right-hand column.
So you need padding. Oh, and asymmetric reversal, as Joachim said.
Here's my revawk:
#!/usr/bin/awk -f
#
length($0)>max {
max=length($0);
}
{
# Reverse the line...
for(i=length($0);i>0;i--) {
o[NR]=o[NR] substr($0,i,1);
}
}
END {
for(i=1;i<=NR;i++) {
# prepend the output with sufficient padding
fmt=sprintf("%%%ds%%s\n",max-length(o[i]));
printf(fmt,"",o[i]);
}
}
(I did this in gawk; I don't think I used any gawkisms, but if you're using a more classic awk variant, you may need to adjust this.)
Use this the same way you'd use rev.
ghoti#pc:~$ echo hello | cowsay | ./revawk | tr '[[]()<>/\\]' '[][)(><\\/]'
_______
< olleh >
-------
^__^ /
_______/(oo) /
/\/( /(__)
| w----||
|| ||
If you're moved to do so, you might even run the translate from within the awk script by adding it to the last printf line:
printf(fmt," ",o[i]) | "tr '[[]()<>/\\]' '[][)(><\\/]'";
But I don't recommend it, as it makes the revawk command less useful for other applications.

Answer 2

Your lines aren't the same length, so reversing the cow will break it. What you need to do is to "pad" the lines to be the same length, then reverse.
For example;
cowsay <<<"hello" | awk '{printf "%-40s\n", $0}' | rev
will pad it to 40 columns, and then reverse.
EDIT: #ghoti did a script that sure beats this simplistic reverse, have a look at his answer.

Answer 3

Here's one way using GNU awk and rev
Run like:
awk -f ./script.awk <(echo "hello" | cowsay){,} | rev
Contents of script.awk:
FNR==NR {
if (length > max) {
max = length
}
next
}
{
while (length < max) {
$0=$0 OFS
}
}1
Alternatively, here's the one-liner:
awk 'FNR==NR { if (length > max) max = length; next } { while (length < max) $0=$0 OFS }1' <(echo "hello" | cowsay){,} | rev
Results:
_______
> olleh <
-------
^__^ \
_______\)oo( \
\/\) \)__(
| w----||
|| ||
----------------------------------------------------------------------------------------------
Here's another way just using GNU awk:
Run like:
awk -f ./script.awk <(echo "hello" | cowsay){,}
Contents of script.awk:
BEGIN {
FS=""
}
FNR==NR {
if (length > max) {
max = length
}
next
}
{
while (length < max) {
$0=$0 OFS
}
for (i=NF; i>=1; i--) {
printf (i!=1) ? $i : $i ORS
}
}
Alternatively, here's the one-liner:
awk 'BEGIN { FS="" } FNR==NR { if (length > max) max = length; next } { while (length < max) $0=$0 OFS; for (i=NF; i>=1; i--) printf (i!=1) ? $i : $i ORS }' <(echo "hello" | cowsay){,}
Results:
_______
> olleh <
-------
^__^ \
_______\)oo( \
\/\) \)__(
| w----||
|| ||
----------------------------------------------------------------------------------------------
Explanation:
Here's an explanation of the second answer. I'm assuming a basic knowledge of awk:
FS="" # set the file separator to read only a single character
# at a time.
FNR==NR { ... } # this returns true for only the first file in the argument
# list. Here, if the length of the line is greater than the
# variable 'max', then set 'max' to the length of the line.
# 'next' simply means consume the next line of input
while ... # So when we read the file for the second time, we loop
# through this file, adding OFS (output FS; which is simply
# a single space) to the end of each line until 'max' is
# reached. This pad's the file nicely.
for ... # then loop through the characters on each line in reverse.
# The printf statement is short for ... if the character is
# not at the first one, print it; else, print it and ORS.
# ORS is the output record separator and is a newline.
Some other things you may need to know:
The {,} wildcard suffix is a shorthand for repeating the input file name twice.
Unfortunately, it's not standard Bourne shell. However, you could instead use:
<(echo "hello" | cowsay) <(echo "hello" | cowsay)
Also, in the first example, { ... }1 is short for { ... print $0 }
HTH.

Answer 4

You could also do it with bash, coreutils and sed (to make it work with zsh the while loop needs to be wrapped in tr ' ' '\x01' | while ... | tr '\x01' ' ', not sure why yet):
say=hello
longest=$(cowsay "$say" | wc -L)
echo "$say" | rev | cowsay | sed 's/\\/\\\\/g' | rev |
while read; do printf "%*s\n" $longest "$REPLY"; done |
tr '[[]()<>/\\]' '[][)(><\\/]'
Output:
_______
< hello >
-------
^__^ /
_______/(oo) /
/\/( /(__)
| w----||
|| ||
This leaves a lot of excess spaces at the end, append | sed 's/ *$//' to remove.
Explanation
The cowsay output needs to be quoted, especially the backslashes which sed takes care of by duplicating them. To get the correct line width printf '%*s' len str is used, which uses len as the string length parameter. Finally asymmetrical characters are replaced by their counterparts, as done in ghoti's answer.

Answer 5

I don't know if you can do this in AWK, but here are the needed steps:
Identify the length of your original's most lengthy line, you will need it give proper spacing to any smaller lines.
(__)\ )\/\
For the last char on each line, map out the need of start-of-line spaces based on what you acquired from the first step.
< hello >
//Needs ??? extra spaces, because it ends right after '>'.
//It does not have spaces after it, making it miss it's correct position after reverse.
(__)\ )\/\
< hello >???????????????
For each line, apply the line's needed number of spaces, followed by the original chars in reverse order.
_______
> olleh <
-------
^__^ \
_______\)oo( \
\/\) \)__(
| w----||
|| ||
Finally, replace all characters that are not horizontally symmetrical with their horizontally-opposite chars. (< to >, [ to ], etc)
_______
< olleh >
-------
^__^ /
_______/(oo) /
/\/( /(__)
| w----||
|| ||
Two things to watch out for:
Text, as you can see, will not go right with reversions.
Characters like $, % and & are not horizontally symmetrical,
but also might not have an opposite unless you use specialized
Unicode blocks.

Answer 6

I would say that you may need each line to be fixed column width so each line is the same length. So if the first line is a character followed by a LF, you'll need to pad the reverse with white space before reversing.