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Often, the first thing you (or your boss) want to know about your sequencing run is simply, "how many reads are there?". For the $BI/gva_course/mapping/data/SRR030257_1.fastq file, the answer is 3,800,180. How can we figure that out?
The grep (or Global Regular Expression Print) command can be used to determine the number of lines which match some criteria as shown above. Above we used it to search for:
- anything from the group of ACTGN with the [] marking them as a group
- matching any number of times *
- from the beginning of the line ^
- to the end of the line $
Here, since we are only interested in the number of reads that we have, we can make use of knowing the 3rd line in the fastq file is a + and a + only, and grep's -c option to simply report the number of reads in a file.
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| language | bash |
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| title | Can you use the information above to write a grep command to count the number of reads in the same file? |
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| collapse | true |
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grep -c "^+$" $BI/gva_course/mapping/data/SRR030257_1.fastq
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In our first tutorial we mentioned how knowing what version of a program you are using can be. When we installed the the cutadapt package we didn't specify what version to install. Can you figure out what version you used, and what the most recent version of the program there is? . | Expand |
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| title | How to figure out the currently installed version |
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| try using the program's help files, or conda's list function | Code Block |
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| language | bash |
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| title | Still not sure? |
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| collapse | true |
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| cutadapt --version
conda list
conda list cutadapt |
Note that all 3 of the above commands will give you the same answer: 1.18 |
Figuring out the most recent version is a little more complicated. Unlike programs on your computer like Microsoft Office or your internet browser, there is nothing in an installed program that tells you if you have the newest version or even what the newest version is. If you go to the programs website (easily found with google or this link), the changes section lists all the versions that have been list with v3v4.4 1 being released on March 30th the 7th of this yearmonth. | Expand |
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| title | click here for information regarding why there is such a large discrepancy |
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| If you were to look at the labels section of https://anaconda.org/bioconda/cutadapt you you would see that both v3v4.4 1 and v1.18 are available. Since we didn't specify a version, conda tried to figure out what would work best. If you were to play around with removing the cutadapt package and attempt to force v3v4.4 1 to be installed you would eventually come to find that there is a conflict between the python version we have installed (3.7.10) which is higher than the allowed python versions available with V3.4linux-64 glibc program required with V4.1. Cutadapt version 1.18 however does not have such requirements for installation and therefore was installed as the only available option.
To install the 34.4 1 version of cutadapt via conda, we would have to explicitly specify both the version of cutadapt that we wanted (34.41) as well as a compatible version of python (less than 3.7)of glibc. The point of using conda is that it is supposed to make installing programs easier, and having to hunt through error messages is anything but easy. This is simplified by specifying an additional conda channel "conda-forge". Given that the version 1.18 did the job, it is not likely to be worth the effort to update the cutadapt version. , but if you wanted to:
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| language | bash |
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| title | Easiest known solution to installing version 4.1 of cutadapt |
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| conda install -c bioconda cutadapt=4.1 -c conda-forge |
We will discuss conda-forge further in later tutorials.
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This won't be the last time we mention different program versions. |
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