Specifying -r causes tail to print lines from the end of the file in reverse order. The default for -r is to print the entire file this way. Specifying -f causes tail not to quit at the end of the file, but rather to reread the file repeatedly useful for watching a "growing" file such as a log file.
For example, given a file containing the English alphabet with each letter on a separate line, the command:. You can use tail with pipes. For example, to see the sizes of the last few files in the current directory, you could enter at the Unix prompt:. Thanks for ur help Will u b plzzzzzzzzz explain me the program how it works give me in detail explanation bcoz im very much new for shell scripting Once again Tanx in advance.
HI once again Tanx for ur code but still im unable to recover from my problem c i have a file name-myfile it contains the data give below Code :. How to read a file starting at certain line number? I am new to ksh scripts. I would like to be able to read a file line by line from a certain line number. How to read a number from a file? Raffenetti 2 integral format. Read line with particular number of lines. Hi all, I have a file sample.
When reading a csv file, counter to read 20 lines and wait for minute then read next 20 till end. Hello All, i am a newbie and need some help when reading a csv file in a bourne shell script. I want to read 10 lines, then wait for a minute and then do a reading of another 10 lines and so on in the same way. I want to do this till the end of file. Any inputs are appreciated How to read contents of a file from a given line number upto line number again specified by user. Hello Everyone.
I am trying to display contains of a file from a specific line to a specific line let say, from line number 3 to line number 5. Read directory files and count number of lines. Skip to content. Change Language. Related Articles. Table of Contents. Improve Article. Save Article. This will access the file twice. The -f parameter tells grep to get the search pattern from file, in this case stdin by using a dash as the value to the f parameter which is the single randomly selected line from the file.
Indeed, this will not guarantee an output of the requested number of lines if the random selection is so far down that there aren't enough lines left when selecting the block. This would grab all the lines in the file except the last n lines and then shuffle that list of lines. This would ensure that grep can always select the requested number of lines. As mentioned in the accepted answer, GNU shuf supports simple random sampling shuf -n quite well. If sampling methods beyond those supported by shuf are needed, consider tsv-sample from eBay's TSV Utilities.
It supports several additional sampling modes, including weighted random sampling, Bernoulli sampling, and distinct sampling. Performance is similar to GNU shuf both are quite fast.
Disclaimer: I am the author. My sample tool will only use 8 bytes per line, which means that very large files can be sampled from with much less memory. In contrast, the shuf and other tools mentioned above can read the entire file into system memory, which can often lead to out-of-memory errors. Sign up to join this community. The best answers are voted up and rise to the top.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How to randomly sample a subset of a file Ask Question. Asked 8 years ago. Active 1 year, 1 month ago. Viewed 65k times. Improve this question. Timo 5, 24 24 silver badges 27 27 bronze badges. Every line gets the same probability to be chosen. Don't need to be consecutive although there is a tiny probability that a consecutive block of lines be chosen together.
I've updated my question to clearer about that. My github.
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