Common
SY-SUBRC  X(4) Return code. 0 : Ok.

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Program and Transaction
SY-REPID  C(8) Program: Name of ABAP/4 program.
SY-CPROG  C(8) Runtime: Main program.
SY-TCODE  C(4) Session: Current transaction code.
SY-SLSET  C(14) Name of selection set (variant).
SY-BATCH  C(1) 'X' => Background active (transaction is running in a batch environment in background mode).
SY-BINPT  C(1) 'X' => Batch Input (Background or Foreground) active, that is transaction is not called by online user.
SY-CALLD  C(1) 'X' => Call Mode Active (transaction is called from another transaction).
SY-DYNNR  C(4) Number of current screen.
SY-DATAR  C(1) Flag: Data Received. That is user has modified or entered new data on the screen (can by used in PAI for user actions analysis).
Session
SY-LANGU  C(1) SAP logon language key.
SY-UNAME  C(12) Session: SAP user from SAP logon.
SY-HOST  C(8) Host.
SY-SAPRL  C(4) R/3 System, system release.
SY-SYSID  C(8) R/3 System, system Id.
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Date and Time
SY-DATUM  D System: Date. YYYYMMDD. (Appl.Server)
SY-UZEIT  T System: Time. HHMMSS. (Appl.Server)
SY-DATLO  D Local date of user
SY-TIMLO  D Local time of user
SY-ZONLO  D Time zone of user
SY-FDAYW  X(1) Factory Calendar Date: Number of week day.
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Character Strings Processing
SY-FDPOS  X(4) ? Comparisons with Character Strings and Numeric Strings: Offset or string length.
                                    ? SEARCH string statement: Offset of found substring.
                                    ? SEARCH internal table statement: Offset of found substring in the table line.
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Messages Handling
SY-MSGID  C(2) Message Id.
SY-MSGTY  C(1) Message Type.
SY-MSGNO  N(3) Message Number.
SY-MSGV1
SY-MSGV2
SY-MSGV3
SY-MSGV4  C(50) Message Variables.
SY-MSGLI  C(60) Message Line. If after calling a method of an OLE2 Object sy-subrc=1 (that is system error occured while communicating with the presentation server), then this field should contain short description of the error.
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Lists Processing
Current parameters of the report:
SY-LINSZ  X(4) Current line size of the report.
SY-LINCT  X(4) Current page length of the report.
SY-VLINE  C(1) Current vertical line character ('|').
SY-ULINE  C(255) Current horizontal line characters ('-...-').
SY-VAR0
SY-VAR1
SY-VAR2
SY-VAR3
SY-VAR4
SY-VAR5
SY-VAR6
SY-VAR7
SY-VAR8
SY-VAR9  C(20) Current placeholders in the list header (usually &0...&9).
Parameters of the current window:
SY-SCOLS  X(4) Line size of the current window.
SY-SROWS  X(4) Number of lines in the current window.
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List Status:
SY-TITLE  C(70) Title of the current list.
SY-PFKEY  C(8) F key status of the displayed list.
SY-LSIND  X(4) Index of list created by current event (basic list = 0, 1st details list = 1, ...).
Information about the list from which the event was triggered:
SY-LISTI  X(4) Index of the list level from which the event was triggered (index of this list). Usually SY-LSIND - 1.
SY-UCOMM  C(70) Function code that triggered the event.
SY-LILLI  X(4) Absolute number in the displayed list of the line from which the event was triggered.
SY-LISEL  C(255) Contents of the line from which the event was triggered.
SY-CUROW  X(4) Position of the line in the WINDOW from which the event was triggered (counting starts with 1).
SY-CUCOL  X(4) Position of the column in the WINDOW from which the event was triggered (counting starts with 2).
SY-CPAGE  X(4) Page number of the 1st displayed page of the list from which the event was triggered.
SY-STARO  X(4) Number of the 1st line of the 1st page displayed of the list from which the event was triggered (counting starts with 1). Possibly, a page header occupies this line.
SY-STACO  X(4) Number of the 1st column displayed in the list from which the event was triggered (counting starts with 1).
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Current output position:
SY-PAGNO  X(4) Current page number.
SY-LINNO  X(4) Line number on the current page of the current output position.
SY-COLNO  X(4) Column of the current output position.
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Internal Tables Processing
SY-TABIX  X(4) Current index (after APPEND, COLLECT, READ TABLE operations, while LOOP processing).
SY-FDPOS  X(4) SEARCH internal table statement: Offset of found substring in the table line.
SY-TFILL  X(4) Current number of lines  After DESCRIBE TABLE, LOOP AT, and READ TABLE
SY-TLENG  X(4) Current length of lines  
SY-TOCCU  X(4) Initial main memory allocated to the internal table 
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Loops Processing
SY-INDEX  X(4) Current index (in DO, WHILE blocks).
Open SQL
SY-DBCNT  X(4) Number of lines affected or already been processed by the Open SQL operation.
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Screens Processing
SY-STEPL  X(4) Index of the screen table row that is currently being processed. Has a meaning only inside LOOP...ENDLOOP (looping through currently displayed rows of screen table and calling PBO/PAI modules).
SY-LOOPC  X(4) Total number of screen table lines currently displayed on the screen.
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Printing to Spool
SY-PEXPI  N(1) Print parameters, spool retention period
SY-PRIMM  C(1) Print parameters, print immediately
SY-PRREL  C(1) Print parameters, delete after printing
SY-PRBIG  C(1) Print parameters, selection cover page
SY-PRNEW  C(1) Print parameters, new spool request
SY-PDEST  C(4) Print parameters, output device
SY-PLIST  C(12) Print parameters, name of spool request
SY-PRDSN  C(6) Print parameters, name of spool dataset
SY-CALLR  C(8) Print list, ID for print dialog function (e.g. NEW-PAGE)
SY-PTITL  C(70) Print parameters, title of print program
SY-PRREC  C(12) Print parameters, recipient
SY-PRTXT  C(68) Print parameters, text for cover page
SY-PRABT  C(12) Print parameters, department on cover page
SY-PAART  C(16) Print parameters, print formatting
SY-PRCOP  N(3) Print parameters, number of copies
SY-SPONO  N(10) Print list, spool number