Change File's Numbers Bash

Renaming files in a folder to sequential numbers

Try to use a loop, let, and printf for the padding:

a=1
for i in *.jpg; do
  new=$(printf "%04d.jpg" "$a") #04 pad to length of 4
  mv -i -- "$i" "$new"
  let a=a+1
done

using the -i flag prevents automatically overwriting existing files, and using -- prevents mv from interpreting filenames with dashes as options.

Bash change filenames from month name to month number

Assuming you have the GNU version of date(1), you could use date -d to map the month names to numbers:

for f in *.pdf; do 
  IFS=- read y m d <<<"${f%.pdf}"
  mv "$f" "$(date -d "$m $d, $y" +%F.pdf)"
done

I doubt it's any more efficient than your sed -e 's/January/01/' -e 's/February/02/' etc, but it does feel less tedious to type. :)

Explanation:

Loop over the .pdf files, setting f to each filename in turn.
The read line is best explained right to left:

a.
"${f%.pdf}" expands to the filename without the .pdf part, e.g. "2020-August-15".

b. <<< turns that value into a here-string, which is a mechanism for feeding a string as standard input to some command. Essentially, x <<<y does the same thing as echo y | x, with the important difference that the x command is run in the current shell instead of a subshell, so it can have side effects like setting variables.

c. read is a shell builtin that by default reads a single line of input and assigns it to one or more shell variables.

d. IFS is a parameter that tells the shell how to split lines up into words. Here we're setting it – only for the duration of the read command – to -. That tells read to split the line it reads on hyphens instead of whitespace; IFS=- read y m d <<<"2020-August-15" assigns "2020" to y, "August" to m, and "15" to d.
The GNU version of date(1) has a -d parameter that tells it to display another date instead of the current one. It accepts a number of different formats itself, sadly not including "yyyy-Mon-dd", which is why I had to split the filename up with read. But it does accept "Mon dd, yyyy", so that's what I pass to it. +%F.pdf tells it that when it prints the date back out it should do so ISO-style as "yyyy-mm-dd", and append ".pdf" to the result. ("%F" is short for "%Y-%m-%d"; I could also have used -I instead of +anything and moved the .pdf outside the command expansion.)

f. The call to date is wrapped in $(...) to capture its output, and that result is used as the second parameter to mv to rename the files.

How to rename files in bash to increase number in name?

If you can get hold of the Perl-flavoured version of rename, that is simple like this:

rename -n 's/(\d+)/$1 + 100/e' *fasta

Sample Output

'Ciprianus_maximus_11_fred.fasta' would be renamed to 'Ciprianus_maximus_111_fred.fasta'
'Ciprianus_maximus_300_fred.fasta' would be renamed to 'Ciprianus_maximus_400_fred.fasta'
'Ciprianus_maximus_3900_fred.fasta' would be renamed to 'Ciprianus_maximus_4000_fred.fasta'

If you can't read Perl, that says... "Do a single substitution as follows. Wherever you see a bunch of digits next to each other in a row (\d+), remember them (because I put that in parentheses), and then replace them with the evaluated expression of that bunch of digits ($1) plus 100.".

Remove the -n if the dry-run looks correct. The only "tricky part" is the use of e at the end of the substitution which means evaluate the expression in the substitution - or I call it a "calculated replacement".

Rename files with incrementing number starting at certain number

This should work:

for f in *.ABC; do
   num=$(basename "$f" .ABC)
   num2=$(printf "%05d" $((num + 55)))
   echo mv "$f" "$num2.ABC"
done

Notes:

I am assuming your files all follow the pattern of digits followed by .ABC, so that basename $f .ABC extracts the number. You'll have to adjust the num= line if this assumption does not hold.
$(( ... )) is the bash syntax to do arithmetic operations.
(printf "%05d" ...) is here to pad zeroes in front of the number, otherwise you'd just get 55 etc.
Remove the echo once you're convinced it's doing the right thing.
EDIT Warning: the new set of filenames should not overlap the old set of filenames, or you might lose some files. Carefully choosing the order the mv commands are run could solve the issue, but putting the files in a new directory as they are renamed and moving them back after would be much simpler.

EDIT:

@MarkSetchell pointed out in the comments that you want sequential numbering that is not based on the original file names, in which case this loop would work instead:

i=55 # choose your starting destination file number here
for f in *.ABC; do
   dest=$(printf "%05d" $i).ABC
   echo mv "$f" "$dest"
   i=$((i + 1))
done

Is it possible to change a number of filenames to be the file extension in bash?

One solution is to use a for loop to cycle through the files beginning with "$FILENAME", e.g.

for f in "$FILENAME"*
do
    mv "$f" "${f##*.}"
done

Or, as a one-liner:

for f in "$FILENAME"*; do mv "$f" "${f##*.}"; done

Bash script to rename files and increment number in the file name by N

This should work

filename=$1 #Filename
filenumber=$2 #file number from where you want to rename. 
count=$3 #number of files
lastfile=$4 #Last filenumber in the folder

for ((i=lastfile; i>=$filenumber; i--))
do
     mv $filename$i $filename`expr $i + $count`
done

You can run it like below

./rename wizard 15 3 30

Replace numbers in a file name in unix (BASH)

Most probably this one could be fine :)

# printf is used to emulate a lot of files
for f in $( printf "company_red%03d.p12\n" {1..150} )
do
    # get the filename
    n="$f"
    # remove extension
    n="${n%.*}"
    # remove leading letters
    n="${n##*[[:alpha:]]}"
    # add 24, 10# is used to consider the 10-based number
    n="$(( 10#$n + 24 ))"
    # construct new filename
    g="red${n}.p12"
    echo mv "$f" "$g"
done

And this could be simplified a bit

for f in $( printf "company_red%03d.p12\n" {1..150} )
do
    # take the number from the specific, fixed position
    n="${f:11:3}"
    # everything below is the same as in the previous example
    n="$(( 10#$n + 24 ))"
    g="red${n}.p12"
    echo mv "$f" "$g"
done

And finally, this could be simplified yet twice -- just escape of using $n and $g:

for f in $( printf "company_red%03d.p12\n" {1..150} )
do
    echo mv "$f" "red$(( 10#${f:11:3} + 24 )).p12"
done

But this could complicate understanding and supporting of the code.