Need help decyphering ksh script
Here is a piece of ksh script I am trying to understand. I understand that the script reads a file line by line and puts the first part of each line into a variable, whenever third part of each line equals to "Y".
I just have a few questions about parts of the script. Script is as follows:
some questions I have are:
1) in line 5 "case $LINE in", what does it check? Ususally, in other languages, case statement checks multiple cases if a variable equals to some value. here I do not completely understand it
2) In line 7 there is "\#*)" - what does it mean?
3) In line 9 - ";;" what are the two semicolons?
4) in line 11 "*)" ?
5) In line 14:
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
what is the ` in front of echo do, what is awk-F:
and why '{print $3}' cannot be replaced by just $3?
6) In line 20 what does the if statement check for?
if [ "$MYVAR" = '*' ]
I'd really appreciate some help, I am new to ksh scripting
I just have a few questions about parts of the script. Script is as follows:
cat $FILE1 | while read LINE
do
case $LINE in
\#*) # Comment-Line in FILE1
;;
*) # Setup MYVAR
# if third field in FILE1 is 'Y'
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
then
MYVAR=`echo $LINE | awk -F: '{print $1}' -`
if [ "$MYVAR" = '*' ]
then
MYVAR=""
fi
...
esac # End case $LINE
done # End Loop read FILE1some questions I have are:
1) in line 5 "case $LINE in", what does it check? Ususally, in other languages, case statement checks multiple cases if a variable equals to some value. here I do not completely understand it
2) In line 7 there is "\#*)" - what does it mean?
3) In line 9 - ";;" what are the two semicolons?
4) in line 11 "*)" ?
5) In line 14:
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
what is the ` in front of echo do, what is awk-F:
and why '{print $3}' cannot be replaced by just $3?
6) In line 20 what does the if statement check for?
if [ "$MYVAR" = '*' ]
I'd really appreciate some help, I am new to ksh scripting
man awk
NAME
awk - pattern-directed scanning and processing language
SYNOPSIS
awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ file ... ]
DESCRIPTION
Awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more
files specified as -f progfile. With each pattern there can be an associated action that will be performed when a line of
a file matches the pattern. Each line is matched against the pattern portion of every pattern-action statement; the asso-
ciated action is performed for each matched pattern. The file name - means the standard input. Any file of the form
var=value is treated as an assignment, not a filename, and is executed at the time it would have been opened if it were a
filename. The option -v followed by var=value is an assignment to be done before prog is executed; any number of -v
options may be present. The -F fs option defines the input field separator to be the regular expression fs.
An input line is normally made up of fields separated by white space, or by regular expression FS. The fields are denoted
$1, $2, ..., while $0 refers to the entire line. If FS is null, the input line is split into one field per character.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always matches. Pattern-action statements are separated by
newlines or semicolons.
NAME
awk - pattern-directed scanning and processing language
SYNOPSIS
awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ file ... ]
DESCRIPTION
Awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more
files specified as -f progfile. With each pattern there can be an associated action that will be performed when a line of
a file matches the pattern. Each line is matched against the pattern portion of every pattern-action statement; the asso-
ciated action is performed for each matched pattern. The file name - means the standard input. Any file of the form
var=value is treated as an assignment, not a filename, and is executed at the time it would have been opened if it were a
filename. The option -v followed by var=value is an assignment to be done before prog is executed; any number of -v
options may be present. The -F fs option defines the input field separator to be the regular expression fs.
An input line is normally made up of fields separated by white space, or by regular expression FS. The fields are denoted
$1, $2, ..., while $0 refers to the entire line. If FS is null, the input line is split into one field per character.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always matches. Pattern-action statements are separated by
newlines or semicolons.
ASKER
ozo, could you tell me what exactly each line here does?
case $LINE in
\#*)
;;
case $LINE in
\#*)
;;
man [
NAME
test, [ -- condition evaluation utility
SYNOPSIS
test expression
[ expression ]
DESCRIPTION
The test utility evaluates the expression and, if it evaluates to true, returns a zero (true) exit status; otherwise it
returns 1 (false). If there is no expression, test also returns 1 (false).
All operators and flags are separate arguments to the test utility.
The following primaries are used to construct expressions:
...
s1 = s2 True if the strings s1 and s2 are identical.
NAME
test, [ -- condition evaluation utility
SYNOPSIS
test expression
[ expression ]
DESCRIPTION
The test utility evaluates the expression and, if it evaluates to true, returns a zero (true) exit status; otherwise it
returns 1 (false). If there is no expression, test also returns 1 (false).
All operators and flags are separate arguments to the test utility.
The following primaries are used to construct expressions:
...
s1 = s2 True if the strings s1 and s2 are identical.
case $LINE in
\#*)
;;
terminates the case statement if $LINE matches the pattern \#*
\#*)
;;
terminates the case statement if $LINE matches the pattern \#*
ASKER
and what is this pattern?
based on help files I've read, \ makes following characters insignificant
# ia a comment and * I didn't find
what it the pattern "\#*"??
I have read the help file but it was not helpful enough to help me understand the code, that's why i asked the question here. please do not post anymore quotes from help files. Thank you
based on help files I've read, \ makes following characters insignificant
# ia a comment and * I didn't find
what it the pattern "\#*"??
I have read the help file but it was not helpful enough to help me understand the code, that's why i asked the question here. please do not post anymore quotes from help files. Thank you
ASKER
As I understand, if [ "$MYVAR" = '*' ] checks if any value is assigned to MYVAR. Is that correct? If so, why not just say if $MYVAR is not null?
ASKER
Also I think I got this part:
case $LINE in
\#*) # Comment-Line in FILE1
;;
*)
it checks if content of $LINE is a comment - contains #, where \ ensures that compiler does not take the rest of the line for a comment, and if the $LINE is, in fact a comment, it breaks out of the case statement.
*) means if it is anything else, but the comment
case $LINE in
\#*) # Comment-Line in FILE1
;;
*)
it checks if content of $LINE is a comment - contains #, where \ ensures that compiler does not take the rest of the line for a comment, and if the $LINE is, in fact a comment, it breaks out of the case statement.
*) means if it is anything else, but the comment
Without quoting the documentation, I can't tell you that * matches any string
If you read the documentation but still don't understand the code, that suggests that there could be something you didn't understand about * matches any string.
If so, we may be able to clarify if you can help us determine the nature of the misunderstanding.
If you read the documentation but still don't understand the code, that suggests that there could be something you didn't understand about * matches any string.
If so, we may be able to clarify if you can help us determine the nature of the misunderstanding.
ASKER
Looks like I figured most of it out with the help of this tutorial:
http://b62.tripod.com/doc/docksh.htm
Now if you could only help me break this one down:
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
echo $LINE would normally print contents of $LINE to the screen but that does not seem to be the case here
Also awk supposedly scans a file for a pattern but what is -F switch? man awk did not tell me much about switches, -F in particular
And why '{print $3}' -`" = "Y" is used to check if the third part of the string is "Y"? why not just use if[ $3 = "Y"] ??
http://b62.tripod.com/doc/docksh.htm
Now if you could only help me break this one down:
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
echo $LINE would normally print contents of $LINE to the screen but that does not seem to be the case here
Also awk supposedly scans a file for a pattern but what is -F switch? man awk did not tell me much about switches, -F in particular
And why '{print $3}' -`" = "Y" is used to check if the third part of the string is "Y"? why not just use if[ $3 = "Y"] ??
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
But why not just use $3="Y"??
And what does -F switch mean in awk command?
And what does -F switch mean in awk command?
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Tintin, what does the carrot do?
Also could you please explain to me what does
`echo $LINE
do in line: if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
and also why
if [ "$MYVAR" = '*' ]
then
MYVAR=""
fi
cannot e re-written as
if [ $MYVAR != ' ' ]
then
MYVAR=""
fi
Also could you please explain to me what does
`echo $LINE
do in line: if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ]
and also why
if [ "$MYVAR" = '*' ]
then
MYVAR=""
fi
cannot e re-written as
if [ $MYVAR != ' ' ]
then
MYVAR=""
fi
ASKER
Tintin, I tried
and didn't get any output at all
I also tried
The exact format of the lines in the input file is
#DBName:/u01/app/oracle/pr
DBName2:/u01/app/oracle/pr
DBName3:/u01/app/oracle/pr
from the above I only want
DBName3:/u01/app/oracle/pr
to be returned since it is not commented out and ends with "Y"
grep "^\*:.*:Y" $FILE1 | while read LINE
do
echo $LINE
done and didn't get any output at all
I also tried
grep "^\*:*:Y" $FILE1 | while read LINE
do
echo $LINE
done grep "*:*:Y" $FILE1 | while read LINE
do
echo $LINE
done The exact format of the lines in the input file is
#DBName:/u01/app/oracle/pr
DBName2:/u01/app/oracle/pr
DBName3:/u01/app/oracle/pr
from the above I only want
DBName3:/u01/app/oracle/pr
to be returned since it is not commented out and ends with "Y"
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Tintin, but it does not necsessary starts with an upper case
ASKER
I just need to ensure that it does not start with # hash sign
grep -v "^\#" ensures the line does not start with # sign, but I also need the line to be in the format "dbname:path:Y"
grep "^[a-z]*:.*:Y" $FILE1
worked for me but only for lowercase and grep "^[A-Z]*:.*:Y" $FILE1
worked only for all uppercase. I need it to be case independent
grep -v "^\#" ensures the line does not start with # sign, but I also need the line to be in the format "dbname:path:Y"
grep "^[a-z]*:.*:Y" $FILE1
worked for me but only for lowercase and grep "^[A-Z]*:.*:Y" $FILE1
worked only for all uppercase. I need it to be case independent
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
but why is
grep "^\*:.*:Y" $FILE1
not working?
and what is the purpose of the dot (.) in the string above, between : and *
grep "^\*:.*:Y" $FILE1
not working?
and what is the purpose of the dot (.) in the string above, between : and *
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Tintin, what would I use to match a line that can start with any character (except #) but contain colon twice and end with Y?
Example: xxx:xxxxxx:Y
I tried
grep "^[!#*]:.*:Y" $FILE1
and
grep "^[!#]*:.*:Y" $FILE1
but neither worked
Example: xxx:xxxxxx:Y
I tried
grep "^[!#*]:.*:Y" $FILE1
and
grep "^[!#]*:.*:Y" $FILE1
but neither worked
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Thank you all!
...
case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the first pattern that matches word. The form of the patterns is
the same as that used for file-name generation (see File Name Generation below). The ;; operator causes execution
of case to terminate. If ;& is used in place of ;; the next subsequent list, if any, is executed.
...
Command Substitution.
The standard output from a command enclosed in parentheses preceded by a dollar sign ( $() ) or a pair of grave accents
(``) may be used as part or all of a word; trailing new-lines are removed. In the second (obsolete) form, the string
between the quotes is processed for special quoting characters before the command is executed (see Quoting below). The
command substitution $(cat file) can be replaced by the equivalent but faster $(<file). The command substitution $(n<#)
will expand to the current byte offset for file descriptor n.