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CS 403: Programming Languages

Lecture 21

Fall 2003

Department of Computer Science

University of Alabama

Joel Jones

Lecture 21 2

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Overview Announcements

Story Hour, Houser 108, 3PM Friday Colloquium, Houser 108, 11PM Monday, received his Ph.D.

from UA. Prof. Nenad Jukic Loyola University Chicago. “Comprehensive Data Warehouse Exploration: Extending the Scope of Association-Rule Mining”

MP2 Shell Programming

Substitution Sub-shells, background mode, job control Quoting Regular Expressions and filters

Final version of which# which cmd: which cmd in PATH is executed, final version

opath=$PATHPATH=/bin:/usr/bin

case $# in0) echo ‘Usage: which command’ 1>&2; exit 2esacfor i in `echo $opath | sed ‘s/^:/.:/ s/::/:.:/g s/:$/:./ s/:/ /g’`do if test -f $i/$1 then echo $i/$1 # found it exit 0 fidoneexit 1 # not found

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$ cat makeHTMLcat << EOF<t>Hello $1 $2</t>EOF$ makeHTML Joel Jones<t>Hello Joel Jones</t>

Another way of doing substitution

In contrast to <<‘s’ which does no substitution

$ cat makeHTML2cat << ‘EOF’<t>Hello $1 $2</t>EOF$ makeHTML2 Joel Jones<t>Hello $1 $2</t>

Programs that write programs$ cat bundle# bundle: group files into distribution packageecho '# to unbundle, sh this file'for ido echo "echo $i 1>&2" echo "cat >$i <<'End of $i'" cat $i echo "End of $i"done$ ./bundle makeHTML makeHTML2 > junk

$ cat junk # to unbundle, sh this fileecho makeHTML 1>&2cat >makeHTML <<'End of makeHTML'cat << EOF<t>Hello $1 $2</t>EOFEnd of makeHTMLecho makeHTML2 1>&2cat >makeHTML2 <<'End of makeHTML2'cat << 'EOF'<t>Hello $1 $2</t>EOFEnd of makeHTML2

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Sub-shells, background mode, and job control$ sleep 5$$ (sleep 5; date) & date[1] 2682Thu Nov 13 00:19:31 CST 2003$ Thu Nov 13 00:19:36 CST 2003$ (sleep 300; echo Tea is ready) &[1] 2684$jobs[1] + Running (sleep 300; echo Tea is ready) &$ kill %1[1] + Terminated (sleep 300; echo Tea is ready) &$

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Some examples of quoting

$ dateThu Nov 13 00:28:08 CST 2003$ echo "The time is `date`"

Pair Up: What is the output?

$ `date`

Pair Up: What is the output?

$ echo `echo \`date\``

Pair Up: What is the output?

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Filters

$ ls -ltotal 32-rwxr--r-- 1 jones staff 203 Nov 13 00:09 bundle-rw-r--r-- 1 jones staff 240 Nov 13 00:10 junk-rwxr--r-- 1 jones staff 34 Nov 13 00:00 makeHTML-rwxr--r-- 1 jones staff 36 Nov 13 00:04 makeHTML2drwxr-xr-x 2 jones staff 68 Nov 13 00:41 subdir$ ls -l | grep ‘^d’

Pair Up: What is the output?

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Regular Expressions and Filters

$ tail -3 /usr/share/dict/web2zythumZyzomysZyzzogeton$

Pair Up: write a grep command to find all words that contain all fives vowels, in order, e.g. abstemious. Format: grep pattern file*

Grep Regular Expressions

c Any non-special character c matches itself

^ Beginning of line

$ End of line

[…] Any one of the characters in …; ranges like a-z are legal

[^…] Any single character not in …; ranges are legal

r* Zero or more occurrences of r

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Pair Up: Write a sort command that prints unique lines doing a case insensitive comparison.

Other Filters Sort has lots of options

-f folds upper and lower case -n sorts by numeric value -r reverses order +m skips first m fields, +0

stands for entire line -u (unique) removes adjacent

duplicate lines

Multiple field specifications do lexigraphic sorting—lines considered equal by earlier sorts are grouped and kept together as subsequent sorts sort each group

sort +0f +0 -u filenames

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Other Filters (cont.) tr inputChars outputChar(s)

tr a-z A-Z maps lower case to upper case Flags: -s squeezes multiple occurences of a

character in the input to a single character in the output; -c takes the complement of the first argument, e.g. tr -c ab matches every character except a and b. tr also understands character ranges.

uniq removes duplicate adjacent lines Flags: -c adds count of duplicate lines at beginning

‘\012’ is a new linePair Up: Write a pipeline that prints the 10 most frequent words in its input.

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Printing 10 most common words

cat $* | # tr doesn’t take filename argumentstr -sc A-Za-z ‘\012’ | # all non alpha become newlinesort |uniq -c | # get the countsort -n | # sort by counttail # prints 10 by default

Use the man command to look at for help man sort