This question already has answers here:
What's the magic of "-" (a dash) in command-line parameters?
(5 answers)
Closed 5 years ago.
I saw this line of code the other day and I didn't know exactly what is this - or when to use it. This is a simple code and from what I understood is that - takes the piped output and treats it as an argument of paste (correct me if I'am wrong)
seq $size | paste - $file
My question is when can we use this and is there another way to do the same thing?
Thanks,
This is documented in the man page for paste which says:
With no FILE, or when FILE is -, read standard input.
That is, paste expects you to give it a filename, but you can instead give it a single - instead, which paste will interpret as it should read data from stdin , your pipe in this case, instead of opening a file and read data from that file.
Related
This question already has answers here:
How to extract date from filename with extenstion using shell script
(2 answers)
Closed 9 months ago.
Here I print the file,
cat testfile.txt
demo_test_file_2022-06-06
i need a output like this
demo_test_file_ 2022-06-06
please help me for splitting the line when numbers present in Linux
thanks in advance
You need to read that file line-by-line into an std::string variable, then use find_first_of to find the first digit.
Then use substr
This question already has an answer here:
Haskell writes '\n' instead of a newline
(1 answer)
Closed 2 years ago.
I'm trying to write a program that writes the pound sign '£' in Haskell, but it outputs '\163' whenever I try to use it. I'm guessing that this is some alphanumeric code, but how do I get it to display what I want it to? I'm writing to the console, when calling a function that returns '£'.
Thank you.
This was solved by using putStrLn, because print and show do not allow for non-ASCII characters to be shown.
This question already has answers here:
bash wildcard n digits
(4 answers)
Closed 2 years ago.
How can I match a more complex pattern when using cat or zcat? For example, I know I can do this:
zcat /var/log/nginx/access.log.*.gz
Which will output all the gzipped access logs to stdin.
What if I want a more complex pattern? Say, all the log files that are between 1-15, e.g. something like this pattern:
zcat /var/log/nginx/access.log.([1-9]|1[0-5]).gz
This results in an unexpected token which is obvious, but I'm not sure how I'd escape the regex in this situation? Maybe I need to pipe ls output to zcat instead?
It depends of course on specifically what pattern you want to match. For the example you have given of log files 1-15, you could use something like
cat /var/log/nginx/access.log.{1..15}.gz
which will complain to stderr if any of those numbers don't exist, but it will still concatenate the rest to stdout.
This technique is a "sequence expression" if you want to look it up - it's a part of brace expansion.
This question already has answers here:
How to rename files without changing extension in Linux 102221.pdf to 102221_name.pdf
(3 answers)
Rename multiple files based on pattern in Unix
(24 answers)
Closed 4 years ago.
I need to rename files in a directory taking out a string of characters that is different with each file but starts the same way. I know how to strip characters from the filename, but how do I preserve the extension? I know it's a variation of a common question but I can't find a answer that fits my exact need.
Redshirts_ep6_dSBHpCsvQ3BfQ7-NNIjXYO4pnHpNMvu7bfvURLF3BSzB_3YOOrBBoNnICTR-hg.mp3
-> Redshirts.mp3
PathsNotTaken_ep6_XWixFER4PJyeozVfcxT96UajpnVI7cRMRhAU4Aj9-rpeacnBleuGY9zCPDe0aQ.mp3
-> PathsNotTaken.mp3
The linux command rename is super helpful here. It can use regex to perform the renaming.
This can probably rewritten a bit, but it appears do to the job here:
rename -n 's/(^[^_]*)_.*/$1.mp3/' *.mp3
Just remove that -n flag to run for for real. Leaving it on is just a test.
This regex says:
Characters at the start of the line ^ that don't contain an underscore [^_] repeated any number of times * are captured into a capture group (^[^_]*) if they are followed by an underscore and any number of any other characters _.*. These are then rewritten by using that first capture group $1 followed by .mp3
This question already has answers here:
How to preserve line breaks when storing command output to a variable?
(2 answers)
Closed 7 years ago.
If I grep our syslogs for a specific term, I get a nice output of those logs matching my term and each entry on a separate line.
If I save that to a variable so I can use it in a script as such:
results=$( grep "term" logs )
echo $results
then all the logs run together and are not human readable.
How can I make it look cleaner so when I do echo $results, I can actually read the output?
Thanks,
Quote it:
echo "$results"
This preserves all the whitespace, instead of using it for word splitting.
In general, you should almost always quote variables, unless you have a specific reason not to.