Best Utility

Byron Rakitzis	       
Princeton University   
5707 Old Lodge Dr.     
Houston, TX 77066      
USA		       

Sean Dorward
Princeton University
10274 Burleigh Cottage Lane
Ellicott City, MD 21043
USA

To build:

    make all

Cody Boone Ferguson fixed this to work with modern compilers; exit(3) returns void but the function was used in a binary expression so this wouldn't even compile. Cody also changed the code to use fgets() instead of gets() so one would not get a warning about the use of gets() at execution which was interspersed with the output. Thank you Cody for your assistance!

For the original version with gets() see the alternative code section below.

Alternative code:

If you wish to see the original source (fixed so it can compile) that uses gets() instead of fgets() you can look at tbr.alt.c. To compile it:

make alt

Use ./tbr.alt instead of ./tbr for this version. You'll likely get a warning about the usage of gets().

To run:

./tbr
# enter some shell commands

NOTE: globs do not work with this entry. Why?

Try:

./tbr
ls -l tbr tbr.c
# notice how the following does not work:
ls tbr*
# try figuring out how this entry works in an editor:
vi tbr.c
# then figure out how to exit vi :-)

What happens if you try using cd - to return to previous directory? What about cd with no args?

Judges' comments:

This program touches on a well known Unix utility, the 6th edition Bourne Shell (/bin/sh), whose original source was considered to be extremely obfuscated by many people (although Steve Bourne might disagree). Did you know that the Bourne Shell source was a major inspiration for the formation of the IOCCC back in 1984?

The author supplied us with a slightly smaller unformatted version of the program which we include below:

    #define D ,close(
    char*c,q[512],m[256],*v[99],**u,*i[3];int f[2],p;main(){for(m[m[60]=m[62]=
    32]=m[*m=124[m]=9]=6;e(-8),gets(1+(c=q))||(exit(0),0);r(0,0))for(;*++c;);}
    r(t,o){*i=i[2]=0;for(u=v+98;m[*--c]^9;m[*c]&32?i[*c&2]=
    *u,u-v^98&&++u:3)if(!m[*c]){for(*++c=0;!m[*--c];);*--u=
    ++c;}u-v^98?strcmp(*u,"cd")?*c?pipe(f),o=f[1]:1,(p=fork())?e(p),o?
    r(o,0)D o)D*f):4,wait(0):(o?dup2(*f,0)D*f)D o):*i?1 D
    0),e(open(*i,0)):5,t?dup2(t,1)D t):i[2]?9 D
    1),e(creat(i[2],438)):2,e(execvp(*u,u))):e(chdir(u[1])*2):6;}
    e(x){x<0?write(2,"?\n$ "-x/4,2),x+1||(exit(1),0):5;}

Author's comments:

Rot13:

Guvf cebtenz vf n ehqvzragnel furyy. Vg qbrf v/b erqverpgvba, cvcrf
naq pq. Vg syntf reebef ba snvyrq puqve'f, bcra'f, perng'f
rkrpic'f, sbex'f naq n srj flagnk reebef.

Guvf cebtenz vf boshfpngrq va n srj abgnoyr jnlf: ncneg sebz gur
ynlbhg (na hasbeznggrq (ohg pehapurq) irefvba vf vapyhqrq sbe
crbcyr jub jnag gb chg guvf guebhtu po) vg znxrf pyrire hfr bs n
jevgr fgngrzrag, fb gung gur fnzr fgngrzrag pna or hfrq gb cevag
reebef naq gur cebzcg. Ol pnyyvat gur reebe shapgvba jvgu gur inyhr
-8, gur cbvagre bssfrg va gur rkcerffvba "?\a$ "-k/4 tbrf sebz 0 gb
2.  Cerfgb!  N cebzcg. Sbe reebef jvgu ahzoref fznyyre guna -4
(v.r., HAVK flfgrz pnyyf) n dhrfgvba znex vf cevagrq.

Gur reebe inyhr bs puqve vf qbhoyrq fb gung jr qba'g rkvg sebz gur
cnerag furyy ba n puqve reebe (fvapr r() rkvgf ba -1 reebef bayl).
Nyy bgure flfgrz pnyy snvyherf rkvg fvapr gurl ner sebz fhofuryyf.

Erphefvba vf farnxvyl rzcyblrq gb nibvq n frpbaq pnyy gb sbex(),
naq gur yvar vf cnefrq va n snveyl ovmneer snfuvba:  onpxjneqf. Gur
urneg bs gur cebtenz, gung vf, gur cneg juvpu cresbezf nyy sbexf,
rkrpf, bcraf, rgp. vf BAR P FGNGRZRAG.

Gur zrgn-inyhrf neenl vf vavgvnyvmrq va n ovmneer snfuvba, naq gur
fhofrdhrag purpxf sbe gur '<' naq '>' ner cresbezrq va n fvatyr
fgngrzrag hfvat n znfx, fvapr lbh xabj gung '>'&2 vf 0, jurernf
'<'&2 vf 2. Bgure fhpu zvpeb-boshfpngvbaf nobhaq.

Svanyyl, vg vf abgnoyr gung gur pbqr jnf unpxrq sbe zvavznyvgl. Vs
lbh ybbx ng gur pbzcerffrq irefvba, lbh jvyy or uneq-cerffrq gb
ryvzvangr zber guna n srj punenpgref (jr pna'g frr ubj gb znxr vg
nal fznyyre!).  550 punenpgref vf cerggl yrna sbe n furyy gung qbrf
guvf zhpu.

OHTF

Gur flagnk bs gur furyy unf abg orra shyyl rkcyberq, ohg vs lbh gel
gb erqverpg va gur fnzr qverpgvba zber guna bapr, bayl bar
erqverpgvba vf cresbezrq. Guvf vf n "srngher" bs gur jnl gur yvar
vf cnefrq; n cbvagre gb gur fgnpx bs nethzragf vf nffvtarq naq na
nethzrag vf fgbyra rirel gvzr n ">" be "<" vf rapbhagrerq.  Gur
furyy syntf na reebe vs ab nethzragf ner ba gur fgnpx. Guhf, sbe
rknzcyr:
	png > sbb > one
pngf gb sbb, fvapr vg jnf chfurq ynfg, ohg
	png > > sbb one
pngf gb one, fvapr one jnf chfurq haqre sbb. (erzrzore jr'er
cnefvat evtug-yrsg)

Qrcraqvat ba lbhe synibe bs HA*K, pq jvgubhg na nethzrag jvyy
rvgure cebqhpr na reebe be whfg qb abguvat.

Gurer vf whfg bar reebe zrffntr, gur dhrfgvba znex, ohg url, gung'f
nyy rq qbrf gbb.

Copyright (c) 1990, Landon Curt Noll & Larry Bassel. All Rights Reserved. Permission for personal, educational or non-profit use is granted provided this this copyright and notice are included in its entirety and remains unaltered. All other uses must receive prior permission in writing from both Landon Curt Noll and Larry Bassel.

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