All UNIX shells cache the command paths based on the contents of PATH enviromental variable. This can cause a problem if a cached path no longer exists. To clear the cached command path, run:
PATH=$PATH
For Bash only, you can run:
hash -r
Another cache is used for the locate command which can be updated by running:
updatedb
Either of two forms:
Functions must appear in the script before they can be used
Local variables defined with local keyword
local [options] [var1[=value]] [var2[=value]] ...
Positional parameters are passed the same way as in scripts. i.e. $1, $2, etc
a=ABCXYZABC
echo ${a/C/w} ==> ABwXYZABC # substitude w for first C
echo ${a//C/w} ==> ABwXYZABw # global substitute
echo ${a:3} ==> XYZABC # substring (zero based)
echo ${a:3:2} ==> XY # position:# of characters
b=''
echo ${b:-word} ==> word
echo ${b:=word} ==> word (also b now = word)
echo ${b:?} ==> b: parameter null or not set (script exits)
echo ${b:?word} ==> b: word (script exits)
echo ${b:+word} ==> b: null
c=ABCXYZABC
echo ${c#*B} ==> CXYZABC # beginning match
echo ${c##*B} ==> C # greedy beginning
echo ${c%B*} ==> ABCXYZA # ending match
echo ${c%%B*} ==> A # greedy ending
This article shows seven methods of writing MySQL database shell scripts.
Start with an appropriate ~/.my.cnf
(see the mysql man page for details)
#!/bin/sh -
# Send a single command to the MySQL server
MYSQL='/usr/bin/mysql'
$MYSQL -sse 'SELECT Artist, Year FROM music'
The -e (execute) switch is required when passing a SQL command on the command line. The -s (silent) switch supresses the ASCII symbol box. Use it twice to supress column headings also. Results are displayed in tab delimited format.
#!/bin/sh -
# Send multiple commands to the MySQL server
MYSQL='/usr/bin/mysql'
$MYSQL <<EOF
SHOW TABLES;
SELECT Artist, Year FROM music;
EOF
#!/bin/sh -
# Redirect MySQL output to a variable
MYSQL='/usr/bin/mysql'
output=$($MYSQL -e 'SELECT Artist, Year FROM music')
for line in "$output"; do
echo "$line"
done
If you want "boxed" output include the --table (-t) option
To supress column headings use the --skip-column-names (-N) option
#!/bin/sh -
# Output MySQL result to a file
MYSQL='/usr/bin/mysql'
$MYSQL -e 'SELECT Artist, Year FROM music' > music.txt
#!/bin/sh -
# Output MySQL result to a file in HTML format
MYSQL='/usr/bin/mysql'
$MYSQL -He 'SELECT Artist, Year FROM music' > music.html
#!/bin/sh -
# Output MySQL result to a file in XML format
MYSQL='/usr/bin/mysql'
$MYSQL -Xe 'SELECT Artist, Year FROM music' > music.xml
#!/bin/sh -
# Using a CGI script to serve MySQL data
mysql=/usr/bin/mysql
user=myself
host=localhost
pass=secret
db=my_database
table=my_table
echo Content-type: text/html
echo ""
echo "<html><head><title>my_title</title></head>"
echo "<body><p align=center>"
$mysql -u$user -h$host --password=$pass -He "SELECT * FROM $table" $db
echo ""
echo "</p></body></html>
"
You can also execute SQL statements in a script file (batch file) like this:
shell> mysql db_name < script.sql > output.tab
By default, when running MySQL queries in batch mode (i.e. with the --batch (-B) option, the output is tab delimited with each row on a separate line, and includes an initial row of column headings. To supress these headings use the --skip-column-names (-N) option. To produce the same kind of "boxed" output you get when running interactively, use the --table (-t) option.
If you have problems due to insufficient memory for large result sets, use the --quick option. This forces mysql to retrieve results from the server a row at a time rather than retrieving the entire result set and buffering it in memory before displaying it.
expr 8 \* 9
echo $[8 * 9]
echo " scale=4; 3.44 / 5 " | bc
echo $(bc << EOF
scale = 4
a1 = (3 + 4)
b1 = (5 + 6)
a1 + b1
EOF
)
let "t2 = ((a = 9, 15 / 3))" # Set "a =9" and "t2 = 15 / 3"
# Convert a base 10 number to base 16
printf %x 65535 --> ffff
Convert a base 16 number to base 10
echo $(( 16#ffff )) --> 65535
To put a list of items in an array
declare -a arr
arr=($(ls -ld))
To get the number of elements
${#arr[*]}
or
${#arr[@]}
if test condition; then if [ condition ]; then if [ ! condition ]; then if [ condition1 ] && [ condition2 ]; then if [ condition1 ] && [ \(condition2 \) -o \(condition3\) ]; then (parenthesis must be escaped)(-a and -o can only be used inside a test) if [[ condition1 ]] || [[ condition2 ]]; then (word splitting and pathname expansion not done)
NOTE: Truth values returned by test (and exit) are 0 for true, 1 for false.
Bash's regular expression comparison operator takes a string on the left and an extended regular expression on the right. It returns 0 (success) if the regular expression matches the string, otherwise it returns 1 (failure).
In addition to doing simple matching, bash regular expressions support sub-patterns surrounded by parenthesis for capturing parts of the match. The matches are assigned to an array variable BASH_REMATCH. The entire match is assigned to BASH_REMATCH[0], the first sub-pattern is assigned to BASH_REMATCH[1], etc..
haystack =~ needle -n string string length > 0 -z string string length = 0 -a file file exists -e file file exists -s file file exists and is not empty -N file file modified since last read Integer conditionals: -lt -le -eq -ge -gt -ne $((...)) is the preferred integer conditional test [ $(((3 > 2) && (4 <= 1))) = 1 ]
NOTE: Truth values returned by $((...)) are 1 for true, 0 for false.
So [ 2 -gt 1 ] && [ $(( 2 < 1 )) ] returns true !!
The read command works one way with the default variable $REPLY and a different way with any other variable name. See for yourself:
while : ; do
read -n 1
case $REPLY in
' ') break;;
*) continue;;
esac
done
Now try with a different variable name:
while : ; do
read -n 1 somevar
case $somevar in
' ') break;;
*) continue;;
esac
done
Pressing the space bar to exit the loop only works in the first example
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| First created Dec 14, 2008 ~ Last revised August 27, 2010 |
