Script started on Mon Nov  9 17:29:00 2026
Restored session: Wed Nov  4 18:45:46 EST 2026
macbook:Desktop> cat q21.txt 
"echo $$" tells us what?
a. the process ID of the shell
b. the number of arguments
c. the last argument
d. a list of all files in the current directory 
  

macbook:Desktop> (sleep 30; echo done 1) &
[1] 42331
macbook:Desktop> (sleep 30; echo done 2) &
[2] 42335
macbook:Desktop> echo done 3; wait; echo done 4
done 3
done 1
[1]  - done       ( sleep 30; echo done 1; )
done 2
[2]  + done       ( sleep 30; echo done 2; )
done 4
%                                                   macbook:Desktop> which vi
/usr/bin/vi
macbook:Desktop> echo $PATH
/Users/mweeks/bin/:/Users/mweeks/programs/myutils:/Users/mweeks/programs:/Users/mweeks/.diversion/bin:/Users/mweeks/Library/Python/3.11/bin:/Users/mweeks/bin/:/Users/mweeks/programs/myutils:/Users/mweeks/programs:/Users/mweeks/.diversion/bin:/Users/mweeks/Library/Python/3.11/bin:/Library/Frameworks/Python.framework/Versions/3.11/bin:/Users/mweeks/.diversion/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/X11/bin:/Library/Apple/usr/bin:/Library/TeX/texbin
macbook:Desktop> cd 
macbook:~> vi vi
macbook:~> chmod 700 vi
macbook:~> ls -l vi
-rwx------  1 mweeks  staff  32 Nov  9 17:57 vi
macbook:~> ./vi
This is not the real vi
macbook:~> vi
macbook:~> vi
macbook:~> cd /usr/bin/
macbook:bin> ls -l vi
lrwxr-xr-x  1 root  wheel  3 Aug 16  2025 vi -> vim
macbook:bin> cd
macbook:~> cd bin
macbook:bin> mv ../vi .
macbook:bin> ./vi
This is not the real vi
macbook:bin> vi
macbook:bin> echo $PATH
/Users/mweeks/bin/:/Users/mweeks/programs/myutils:/Users/mweeks/programs:/Users/mweeks/.diversion/bin:/Users/mweeks/Library/Python/3.11/bin:/Users/mweeks/bin/:/Users/mweeks/programs/myutils:/Users/mweeks/programs:/Users/mweeks/.diversion/bin:/Users/mweeks/Library/Python/3.11/bin:/Library/Frameworks/Python.framework/Versions/3.11/bin:/Users/mweeks/.diversion/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/X11/bin:/Library/Apple/usr/bin:/Library/TeX/texbin
macbook:bin> pwd
/Users/mweeks/bin
macbook:bin> echo x=5
x=5
macbook:bin> eval `echo x=5`
macbook:bin> echo $x
5
macbook:bin> eval "echo x=5"
x=5
macbook:bin> eval 'echo x=5'
x=5
macbook:bin> `pwd`     
zsh: permission denied: /Users/mweeks/bin
macbook:bin> echo `pwd`
/Users/mweeks/bin
macbook:bin> cdd
macbook:Desktop> cd csc3320_Fall2026/programs/unix_ch4
macbook:unix_ch4> grep shift *
script3.csh:shift
macbook:unix_ch4> cat script3.csh 
#!/bin/csh
echo first argument is $1, all args are $*
shift
echo first argument is $1, all args are $*
 
echo " "
echo "Example:"
echo "$ script3.csh a b c d"
echo "first argument is a, all args are a b c d"
echo "first argument is b, all args are b c d" 

macbook:unix_ch4> ./script3.csh hickory oak apple dateript2.bash*  script2.csh*   script3.csh*
first argument is hickory, all args are hickory oak apple date
first argument is oak, all args are oak apple date
 
Example:
$ script3.csh a b c d
first argument is a, all args are a b c d
first argument is b, all args are b c d
macbook:unix_ch4> read v1 v2
date oak
macbook:unix_ch4> echo $v1
date
macbook:unix_ch4> echo $v2
oak
macbook:unix_ch4> ls predef*
zsh: no matches found: predef*
macbook:unix_ch4> cd ../unix_ch5
macbook:unix_ch5> ls predef*    
predefined.sh
macbook:unix_ch5> cat predefined.sh 
echo You passed $# parameters.
echo These are: "$@"
echo process ID of last background process = $!
echo process ID of this shell = $$
notAcommand
echo Last command returned with $? as the status.
macbook:unix_ch5> ./predefined.sh hickory oak apple date
You passed 4 parameters.
These are: hickory oak apple date
process ID of last background process =
process ID of this shell = 43337
./predefined.sh: line 5: notAcommand: command not found
Last command returned with 127 as the status.
macbook:unix_ch5> expr 2 \* 3
6
macbook:unix_ch5> test -e predefined.sh; echo $?
0
macbook:unix_ch5> test -e predefineddoesnotexist.sh;echo $?
1
macbook:unix_ch5> cat testfor.sh 
params=$@
for value in $params
do
  echo param: $value
done

macbook:unix_ch5> ./test
test_file_exists.sh*   testcase2c.sh*         testif.sh*
test_file_exists2../testfor.sh hickory oak apple date
param: hickory
param: oak
param: apple
param: date
macbook:unix_ch5> cat testif.sh
echo "enter a word: "
read v1
if [ -e $v1 ]
then
  echo "A file by that name exists."
else
  echo "No file by that name exists."
fi 
macbook:unix_ch5> ./testif.sh 
enter a word: 
hickory
No file by that name exists.
macbook:unix_ch5> ./testif.sh 
enter a word: 
testfor.sh
A file by that name exists.
macbook:unix_ch5> exit

Saving session...
...saving history...truncating history files...
...completed.
Deleting expired sessions...none found.

Script done on Mon Nov  9 18:45:41 2026


MacOS has an /etc/paths folder
https://stackoverflow.com/questions/22465332/setting-path-environment-variable-in-macos-permanently