Chapter 8 — Input, Output, Pipes and Processes — Solutions

do the assignment first. reading the answer is not the same as doing it, and u will feel like u learned it when u didn’t.

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# 1
ls ~
echo $?
ls ~/nope
echo $?
 
# 2
echo "first line" > notes.log
 
# 3
echo "second line" >> notes.log
cat notes.log
 
# 4
cat missing.txt 2> errors.log
cat errors.log
 
# 5
ls ~ | wc -l
 
# 6
ls ~ | grep "D" | wc -l
 
# 7
ps aux | grep "bash"
 
# 8
mkdir practice && cd practice
 
# 9
sleep 30 &
jobs
fg
# then ctrl + c to kill it
 
# 10
sleep 30
# press ctrl + z
bg
jobs

output of 1:

0
2

output of 3:

first line
second line

output of 4:

cat: missing.txt: No such file or directory

output of 9:

[1] 4517
[1]+  Running                 sleep 30 &
sleep 30

• in step 3, if u used > instead of >> u would have lost first line completely.
• in step 4, notice that nothing appeared on ur screen when u ran the cat. that is the point, the error went into the file instead.
• in step 7, remember one of the lines u see is the grep itself.
• in step 8, && is the answer and ; is the wrong one. if the mkdir fails because the folder already exists, ; would still run the cd.
• in step 10, if u stop after ctrl + z and never type bg, that sleep is paused and not running. jobs would say Stopped instead of Running. try it both ways and look at the difference.

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