UnixNotes_Day2.txt

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Astronomy 300 - Day 2 Notes - Streams, sorting, and AWK
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$ cd
$ cd Astro300-A19
$ git pull

$ cd Data

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Line Numbers

$ nl Jabber.txt          Shows line number
$ nl -ba Jabber.txt      including blank lines (more useful)

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$ cat BrightStars.csv             streams file to terminal

Chopping Streams (head and tail)

$ head BrightStars.csv            first 10 lines
$ tail BrightStars.csv            last 10 lines

$ head -20 BrightStars.csv        first 20 lines
$ tail -20 BrightStars.csv        last 20 lines

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Diverting Streams (> and >>)

$ head -23 BrightStars.csv > 10Bright.csv     (>) crates file, overwriting old
$ ls

$ wc 10Bright.csv                             number of lines, words, and bytes

$ tail -11 BrightStars.csv >> 10Bright.csv    (>>) appends data to file

$ wc 10Bright.csv

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Connecting Streams - pipes (|)

$ cat 10Bright.csv | grep 'e'        <- grep matches thing in ' '
$ cat 10Bright.csv | grep 'e' | wc

$ cat 10Bright.csv | grep -v '^\#' | grep 'e'                 ignore lines beginning with #

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Sorting Streams - sort

$ cat 10Bright.csv | grep -v '^\#' | sort -t ',' -k 2         Alphabetical sort (default)
$ cat 10Bright.csv | grep -v '^\#' | sort -t ',' -k 1         Not good for numbers!
$ cat 10Bright.csv | grep -v '^\#' | sort -t ',' -g -k 1      Numerical sort (very different)
$ cat 10Bright.csv | grep -v '^\#' | sort -t ',' -g -r -k 5   Reverse sort

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AWK - Aho, Weinberger, & Kernighan

$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{print $2}'    print 2nd column
$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{print $0}'    Same as $ cat 10Bright.csv

$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{print $5,$1}'
$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{OFS=","}{print $5,$1}'

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==  equal to         <   less than                   &&  and
!=  not equal to     >=  greater than or equal to    ||  or
>   greater than     <=  less than or equal to

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Print all lines where the value of column 4 > 0.0:
$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{if ($4 > 0.0) print $0}'


Print all lines where the value of column 5 is between 0.0 and 1.0:
$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{if ($5>0.0 && $5<1.0) print $0}'


Print all lines where the value of column 2 contains "A" (anywhere in the column).
$ cat 10Bright.csv | grep -v '^\#' | awk -F, '{if ($2~/A/) print $0}'


You can append '| wc' to the end of each of the above to get a count

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Assignment #1 - Due Wed by 1pm

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The file in the Data folder: **Constellations.csv** contains a list of
the 88 constellations in the sky.

The 5 columns in the files are:
* Name
* Symbol
* RA of center
* Dec of center
* Flag

The Flag column letters are:
* Z = Zodiacal constellation
* A = Ancient Name
* M = Modern Name (after 1603)

## Questions to Answer - On Canvas.

1. List the names of the constellations that are circumpolar as seen
from Seattle (Lat = +47.6).

2. What constellation is closest to the Zenith, as seen from Seattle, on
midnight on the first day of Autumn?