Question

Using UNIX commands (or the terminal application on Mac)

Write the command to retrieve the accessions number from the files called accessions.txt with the following criterion:

1. contain the number 5
2. contain the letter d or e
3. contain the letters d and e in that order
4. contain the letters d and e in that order with a single letter between them
5. contain both the letters d and e in any order
6. start with x or y
7. start with x or y and end with e
8. contain three or more digits in a row
1. end with d followed by either a, r or p

using this file:

accessions.txt

xkn59438
yhdck2
eihd39d9
chdsye847
hedle3455
xjhd53e
45da
de37dp

Answer 1

Commands

a. grep 5 accessions.txt | sed 's/[^0-9]*//g'
b. grep -e d -e e accessions.txt | sed 's/[^0-9]*//g'
c. grep -E "d.*e" accessions.txt | sed 's/[^0-9]*//g'
d. grep -E "d.e" accessions.txt | sed 's/[^0-9]*//g'
e. grep -E "(d.*e|e.*d)" accessions.txt | sed 's/[^0-9]*//g'
f. grep -E "^(x|y)" accessions.txt | sed 's/[^0-9]*//g'
g. grep -E "^(x|y).*e$" accessions.txt | sed 's/[^0-9]*//g'
h. grep -E "[0-9]{3}" accessions.txt | sed 's/[^0-9]*//g'
i. grep -E "d(a|r|p)$" accessions.txt | sed 's/[^0-9]*//g'

Explanation:

The output of each grep command is passed to the same sed command to filter the text for numbers. Refer to regex documentation or leave a comment if you have any queries!

a. just grep 5 from accessions.txt

b. use two patterns by using the -e flag for both

c. .(dot) means any character (only once) so .* (dot)(asterisk) means any number of characters between d and e

d. "d.e" is specified indicating d followed by any character occurring once followed by e

e. Here | (or) is used and the two patterns are provided (one for d followed by e and another for e followed by d)

f. ^ indicates the start of a string. so ^(x|y) indicates a string that begins with either x or y

g. Again ^(x|y) indicates the string begins with either x or y. $ denotes the end of the string. So .*(any number of characters) followed by e at the end

h. [0-9] indicated a digit between 0 and 9. [0-9]{3} means 3 digits occurring together

i. d(a|r|p)$ means a string ending with either da, dr or dp

OUTPUT: