on 15-Oct-2018 (Mon)

Question

In python 3, what is the easy way to sort a list, using "sorted" method, using a custom comparison function (for example, how to sort release_numbers = [1.2, 4.4.4, 1.2.1], using custom "compare" function that compares 1.2 to 1.2.1)?

Answer

sorted(release_numbers, key=functools.cmp_to_key(compare))
^^ note, in python 3, sorted does not have the cmp argument so you have to use the key argument via the functools.cmp_to_key conversion method)
^^ note 2, make sure you have "import functools" in your code

Question

In Linux, for the vi editor, what key do you press to exit from control mode to input mode (and viceversa)?

Answer

ESC

Question

In linux, in bash shell scripting, the while loop syntax is:
while [condition]
[...]
<<some lines of code here>>
[...]

Answer

do
done

Question

In linux, in bash scripting, the while loop sytax is:
while [...]
do
<<some lines of code here>>
done

Answer

[condition]
^^^ note that the condition goes inside square brackets, as it is expression being evaluated for truthiness

Question

In Linux, write a simple bash script that print the numbers from 1 to 4 out to the stdout in a loop (to demonstrate your knowledge of while loop).

Answer

#!/bin/bash
n=1
while [ $n -le 4 ]
do
​​​​​​​    echo $n
    n = $[n+1]
done

​​​​​​​

Question

In linux, in bash scripting, the [...] statement is identical to the while statement except that the reverse logic is applied in the condition clause.

Answer

until

Question

In linux, in bash scripting, for integer comparisons you use things like -le, -gt, -lt, -eq, etc, while for [...] comparisons you use == (or simply =) and !=

Answer

string

Question

In linux, in shell scripting, the [...] construct is often used to take actions on a bunch of files, one at a time.

Answer

for loop

Question

In linux, write simple bash script that goes through and prints name of all files in current directory (to show your knowledge of for loop).

Answer

#!/bin/bash

for file in $(ls)
do
    echo $file
done

[default - edit me]

Question

In linux, in bash scripting, a [...] is used to put two lines of code on the same line (usually used in while/do/done and if/then/fi cluases to combine the while/do and if/then in one line)

Answer

;
^^ semi-colon

Question

In linux, in bash scripting, while loops are inclosed in do/done, while if/else statements are enclosed in [...] / [...]

Answer

if/fi

Question

In linux, in bash scripting, for the if/else statements, if and elif have the [...] keyword after the condition clause while else does not have it.

Answer

then

Question

In linux, in bash scripting, write if cluase where you already have two vars, x and y, and you print "great" if x is greater than y, "less" if x is smaller than y, and "equal" otherwise.

Answer

if [ $x -gt $y ]; then
    echo "great"
elif [ $x -lt $y ]; then
    echo "less"
else
    echo "equal"
fi

Question

In linux, in bash scripting, how do you print out the first command line argument given when script is run (e.g. if you run "./test.sh hello", "hello" would be printed)

Answer

echo $1
^^^ the $1, prints our the first command line argument, $2 the second, $3 the third, etc

Question

In linux, write simple bash script that takes file name as command line argument, and prints out that file name ONLY if that file exists in the current directory (e.g. running "tests.sh test.txt" would print "yes" only if file test.txt exists).

Answer

#!/bin/bash

if [ -e $1 ]; then
   echo "yes"
fi

^^^ not the use of -e to check existance of file, recall $1 is used to access first command line arg

Question

In linux, in shell scripting, if you are in a while, until or for loop, and you want looping to stop (i.e. execution to continue after "done" line), you use the [...] keyword

Answer

break

Question

In linux, in bash scripting, if you are in while/until/for loop and you wan the current loop iteration to end and just go to the next iteration (i.e. start at top of loop), you use the [...] keyword

Answer

continue

Question

In linux, in bash scripting, what is the difference between the break and continue keywords used in loops?

Answer

break will completely exit the loop (and go to after the "done" keyword) while continue will break out of just the current iteration of loop and go to top of loop for next iteration

Question

In linux, bash carries out file name expansions (e.g. *.txt will represent all files that end in .txt"), and this is a process called [...] ing

Answer

globbing

Question

In linux, in bash scripting, you can use the "for in" loop to loop over files, without using the $(ls) command expansion. For example rewrite the following without using $(ls) command expansion:

for file in $(ls *.txt); do
    echo "found another text file!"
done

Answer

for file in *.txt; do
   echo "found another text file!"
done

Question

In linux, in bash scripting, the [...] statement can execute commands based on a word pattern matching decision.

Answer

case

Question

In linux, write simple bash script, using case statement to check for first command line argument, if it is --help or -h print "help", if it is --version or -v print "1.0", otherwise print "unkown choice".

Answer

case $1 in
    --help|-h)
        echo "help"
        ;;
    --version|-v)
        echo "1.0"
        ;;
    *)
        echo "unknown choice"
        ;;
esac

^^ note the esac at end
^^ note the ;; seperating each option statement
^^ note the ) that is each pattern matching condition, also note that the left ( is missing/optional
^^ note the * catch all glob/pattern for the final condition

Question

In linux, in bash scripting, for the case statement, the entire block starts with keyword case and ends with keyword [...]

Answer

esac
^^ case in reverse, similar to if/fi

Question

In linux, in bash scripting, when you have a case statement block, each condition block must close with the [...] syntax

Answer

;;
^^ double semi-colon

Question

In linux, in bash scripts, when using case statement, for each condition clause, the condition is enclosed in [...] , where the left one is optional.

Answer

round brackets
i.e. ")", since left one is optional and usually ommitted.

Question

In linux, write simple shell script function called usage that simply prints our "usage" when called (note: this excersice just checks your recall of function syntax in bash scripting).

Answer

function usage()
{
    echo "usage"
}

^^ note the function keyword
^^ note the function block enclosed in {}

Question

In linux, you have following function defined in your shell script, how do you call it?

function usage ()
{
        echo "Usage:"
        echo "        myprog.sh [--test|--help|--version]"
}

Answer

usage
^^ note that missing ()!!!