Using Executable Programs
When you writ e a program , youll generally need t o m ake it execut able before you can run it . I n Unix, you do t his by set t ing t he execut e file access m odes using t he
chm od com m and:
chmod +x myprog
To run t he program , nam e it on t he com m and line:
myprog
However, if t he program is in your current direct ory, your shell m ight not find it . The shell searches for program s in t he direct ories nam ed in your
PATH
environm ent variable, but for securit y reasons, t he search pat h for Unix shells oft en is deliberat ely
set not t o include t he current direct ory
.
. I n t hat case, you need t o include a leading pat h of
.
t o explicit ly indicat e t he program s locat ion:
.myprog
Som e of t he program s developed in t his book are int ended only t o dem onst rat e a part icular concept and probably never will be run out side your current direct ory, so
exam ples t hat use t hem generally show how t o invoke t hem using t he leading
.
pat h. For program s t hat are int ended for repeat ed use, it s m ore likely t hat youll inst all t hem in a direct ory nam ed in your
PATH
set t ing. I n t hat case, no leading pat h will be necessary t o invoke t hem . This also holds for com m on Unix ut ilit ies such as
chm od , which are inst alled in st andard syst em direct ories. Under Windows, program s are int erpret ed as execut able based on t heir filenam e
ext ensions such as .exe or .bat , so chm od is unnecessary. Also, t he com m and int erpret er includes t he current direct ory in it s search pat h by default , so you should
be able t o invoke program s t hat are locat ed t here wit hout specifying any leading pat h. Thus, if youre using Windows and you want t o run an exam ple com m and t hat
is shown in t his book using
.
, you should om it t he
.
from t he com m and.
1.33.4 Writing Shell Scripts Under Unix
Here is a shell script t hat report s t he current upt im e of t he MySQL server. I t runs a
SHOW STATUS
query t o get t he value of t he
Uptime
st at us variable t hat cont ains t he server upt im e in seconds:
binsh mysql_uptime.sh - report server uptime in seconds
mysql -B -N -e SHOW STATUS LIKE Uptime
The first line of t he script t hat begins wit h is special. I t indicat es t he pat hnam e of t he
program t hat should be invoked t o execut e t he rest of t he script , bin sh in t his case. To use t he script , creat e a file nam ed m ysql_upt im e.sh t hat cont ains t he preceding lines and m ake it
execut able wit h chm od + x. The m ysql_upt im e.sh script runs m ysql using - e t o indicat e t he query st ring, - B t o generat e bat ch t ab- delim it ed out put , and - N t o suppress t he colum n
header line. The result ing out put looks like t his:
.mysql_uptime.sh Uptime 1260142
The com m and shown here begins wit h
.
, indicat ing t hat t he script is locat ed in your current direct ory. I f you m ove t he script t o a direct ory nam ed in your
PATH
set t ing, you can invoke it from anywhere, but t hen you should om it t he
.
from t he com m and. Not e t hat m oving t he script m ake cause csh or t csh not t o know where t he script is locat ed unt il your next login. To
rem edy t his wit hout logging in again, use rehash aft er m oving t he script . The following exam ple illust rat es t his process:
.mysql_uptime.sh Uptime 1260348
mv mysql_uptime.sh usrlocalbin mysql_uptime.sh
mysql_uptime.sh: Command not found. rehash
mysql_uptime.sh Uptime 1260397
I f you prefer a report t hat list s t he t im e in days, hours, m inut es, and seconds rat her t han j ust seconds, you can use t he out put from t he m ysql
STATUS
st at em ent , which provides t he following inform at ion:
mysql STATUS; Connection id: 12347
Current database: cookbook Current user: cbuserlocalhost
Current pager: stdout Using outfile:
Server version: 3.23.47-log Protocol version: 10
Connection: Localhost via UNIX socket Client characterset: latin1
Server characterset: latin1 UNIX socket: tmpmysql.sock
Uptime: 14 days 14 hours 2 min 46 sec
For upt im e report ing, t he only relevant part of t hat inform at ion is t he line t hat begins wit h
Uptime
. I t s a sim ple m at t er t o w rit e a script t hat sends a
STATUS
com m and t o t he server and filt ers t he out put wit h grep t o ext ract t he desired line:
binsh mysql_uptime2.sh - report server uptime
mysql -e STATUS | grep Uptime The result looks like t his:
.mysql_uptime2.sh Uptime: 14 days 14 hours 2 min 46 sec
The preceding t wo script s specify t he st at em ent t o be execut ed by m eans of t he - e com m and- line opt ion, but you can use ot her m ysql input sources described earlier in t he chapt er, such
as files and pipes. For exam ple, t he following m ysql_upt im e3.sh script is like m ysql_upt im e2.sh but provides input t o m ysql using a pipe:
binsh mysql_uptime3.sh - report server uptime
echo STATUS | mysql | grep Uptime
Som e shells support t he concept of a here-docum ent , which serves essent ially t he sam e purpose as file input t o a com m and, except t hat no explicit filenam e is involved. I n ot her
words, t he docum ent is locat ed right here in t he script , not st ored in an ext ernal file. To provide input t o a com m and using a here-docum ent , use t he following synt ax:
command MARKER
input line 1 input line 2
input line 3
...
MARKER MARKER
signals t he beginning of t he input and indicat es t he m arker sym bol t o look for at t he end of t he input . The sym bol t hat you use for
MARKER
is relat ively arbit rary, but should be som e dist inct ive ident ifier t hat does not occur in t he input given t o t he com m and.
Her e-docum ent s are a useful alt ernat ive t o t he - e opt ion when you need t o specify lengt hy query input . I n such cases, when -e becom es awkward t o use, a here-docum ent is m ore
convenient and easier t o writ e. Suppose you have a log t able
log_tbl
t hat cont ains a colum n
date_added
t o indicat e when each row was added. A query t o report t he num ber of records t hat were added yest erday looks like t his:
SELECT COUNT As New log entries: FROM log_tbl
WHERE date_added = DATE_SUBCURDATE ,INTERVAL 1 DAY;
That query could be specified in a script using - e, but t he com m and line w ould be difficult t o read because t he query is so long. A here- docum ent is a m ore suit able choice in t his case
because you can writ e t he query in m ore readable form : binsh
new_log_entries.sh - count yesterdays log entries
mysql cookbook MYSQL_INPUT SELECT COUNT As New log entries:
FROM log_tbl WHERE date_added = DATE_SUBCURDATE ,INTERVAL 1 DAY;
MYSQL_INPUT
When you use - e or here-docum ent s, you can refer t o shell variables wit hin t he query input — alt hough t he following exam ple dem onst rat es t hat it m ight be best t o avoid t he pract ice.
Suppose you have a sim ple script count _rows.sh for count ing t he rows of any t able in t he
cookbook
dat abase: binsh
count_rows.sh - count rows in cookbook database table require one argument on the command line
if [ -ne 1 ]; then echo Usage: count_rows.sh tbl_name;
exit 1; fi
use argument 1 in the query string mysql cookbook MYSQL_INPUT
SELECT COUNT AS Rows in table: FROM 1; MYSQL_INPUT
The script uses t he shell variable, which holds t he com m and- line argum ent count , and
1
, which holds t he first argum ent aft er t he script nam e. count _rows.sh m akes sure t hat exact ly
one argum ent was provided, t hen uses it as a t able nam e in a row-count ing query. To run t he script , invoke it wit h a t able nam e argum ent :
.count_rows.sh limbs Rows in table:
12
Variable subst it ut ion can be helpful for const ruct ing queries, but you should use t his capabilit y wit h caut ion. A m alicious user could invoke t he script as follows:
.count_rows.sh limbs;DROP TABLE limbs
I n t hat case, t he result ing query input t o m ysql becom es: SELECT COUNT AS Rows in table: FROM limbs;DROP TABLE limbs;
This input count s t he t able rows, t hen dest roys t he t able For t his reason, it m ay be prudent t o lim it use of variable subst it ut ion t o your own privat e script s. Alt ernat ively, rewrit e t he script
using an API t hat allows special charact ers such as
;
t o be dealt w it h and rendered harm less see
Recipe 2.8 .
1.33.5 Writing Shell Scripts Under Windows
