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Top Forums UNIX for Beginners Questions & Answers Help understanding what this ls -l command is checking in a script Post 303039570 by greavette on Wednesday 9th of October 2019 06:17:28 PM
Old 10-09-2019
Help understanding what this ls -l command is checking in a script

Hello,

we have a script that has the two following lines:

Code:
ssh -qno StrictHostKeyChecking=no -o ConnectTimeout=1 user@IP 'ls -l /home/opsmgrsvc >/dev/null 2>&1' > /dev/null 2>&1
 status="$(echo $?)"

I can't understand what these two lines are doing?
When I execute the first line nothing is output. I get that the command is being directed somewhere that is not shown. And when I execute the echo $? line I get a number. Not sure what this number means though? Is this command checking if I can successfully login to this server or not?

Also, is there a way to concatenate the two lines into one command line instruction to return the value?

Thank you.

Last edited by jim mcnamara; 10-09-2019 at 07:37 PM..
 

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Execute(4)						     Kernel Interfaces Manual							Execute(4)

NAME
Execute - Contains instructions for running commands that require the resources of a remote system SYNOPSIS
/usr/spool/uucp/SystemName/X.RemoteSystemNxxxx DESCRIPTION
The Execute (X.*) files contain instructions for running uucp commands that require the resources of a remote system. They are created by the uux command. The full pathname of a uux command execute file is a form of the following: /usr/spool/uucp/SystemName/X.RemoteSystem- Nxxxx where the SystemName directory is named for the local computer and the RemoteSystem directory is named for the remote system. The N char- acter represents the grade of the work, and the xxxx notation is the 4-digit hexadecimal transfer-sequence number; for example, X.zeusN2121. Note that the grade of the work specifies when the file is to be transmitted during a particular connection. The grade notation is a sin- gle number (0 to 9) or letter (A to Z, a to z). Lower sequence characters cause the file to be transmitted earlier in the connection than do higher sequence characters. The number 0 (zero) is the highest grade, signifying the earliest transmittal; z is the lowest grade, sig- nifying the latest transmittal. The default grade is N. Standard Entries in an Execute File An execute file consists of several lines, each with an identification character and one or more entries: Format and Description U UserName SystemName Specifies the login name of the user issuing the uux command and the name of the system from which the command was issued. N or Z Indicates the error status. The N character means that a failure message is not sent to the user issuing the uux command if the specified command does not exe- cute successfully on the remote system. The Z character means that a failure message is sent to the user issuing the uux command if the specified command does not execute successfully on the remote system. R UserName Specifies the login ID of the user requesting the remote command execution. F FileName Contains the names of the files required to execute the specified command on the remote system. The FileName parameter can be either the complete pathname of the file, including the unique transmission name assigned by the uucp program, or simply the trans- mission name without any path information. The Required File Line can contain zero or more filenames. The uuxqt daemon checks for the existence of all listed files before running the specified command. I FileName Specifies the standard input to be used. The standard input is either specified by a < (less than) symbol in the command string, or is inherited from the standard input of the uux command if that command was issued with the - (dash) flag. If standard input is specified, it also is listed in an F (Required File) line. If standard input is not specified, the uucp program uses the /dev/null device file. O FileName SystemName Specifies the names of the file and system that are to receive standard output from the execution of the command. Standard output is specified by a > (greater than) symbol within the command string. (The >> sequence is not valid in uux commands.) As was the case with standard input, if standard output is not specified, the uucp program uses the /dev/null device file. C CommandString This is the command string that the user requests to be run on the specified system. The uucp program checks the /usr/lib/uucp/Per- missions file on the designated computer to see whether the login ID can run the command on that system. All required files go to the execute file directory, usually /usr/spool/uucp/.Xqtdir. After execution, the standard output is sent to the requested location EXAMPLES
User fong on local system zeus enters the following command: uux - "diff /u/fong/out hera!/u/fong/out2 > ~uucp/DF" This invokes the uux command to run a diff command on the local system, comparing file /u/fong/out with file /u/fong/out2, which is stored on remote system hera. The output of the comparison is placed in the DF file in the public directory on the local system. This command produced the /usr/spool/uucp/hera/X.zeusN212F execute file, which contains the following information: U fong zeus # return status on failure Z # return address for status or input return R fong F /usr/spool/uucp/hera/D.herale954fd out2 O ~uucp/DF zeus C diff /u/fong/out out2 The user line identifies user fong on system zeus. The error status line indicates that fong will receive a failure status message if the diff command fails to execute. The requester is fong, and the file required to execute the command is the following data file: /usr/spool/uucp/hera/D.herale954fd out2 The output of the command is to be written to the public directory on system zeus with the filename DF. (Remember that ~uucp is the shorthand way of specifying the public directory.) The final line is the command string that user fong entered with the uux command. The following is another example of an execute file: U uucp hera # don't return status on failure N # return address for status or input return R uucp F D.hera5eb7f7b I D.hera5eb7f7b C rmail fong This indicates that user uucp on system hera is sending mail to user fong, who is also working on system hera. FILES
Describes access permissions for remote systems Describes accessible remote systems Contains uucp command, data, and execute files Contain instructions for transfers Contains lists of commands that remote systems are permitted to execute Contains files that have been trans- ferred RELATED INFORMATION
Daemons: uuxqt Commands: diff(1), uux(1) delim off Execute(4)
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